Pool Shock: Shocking for Algae Removal

shocking for algae removal

Unless you’re an alligator, it’s safe to assume you don’t want to be swimming around in algae. But if you do, we won’t judge! However, for everyone else, an abundance of algae in your swimming pool is the stuff of nightmares. Thankfully, algae has enemies — algaecide and cal-hypo (calcium hypochlorite) shock! These two chemicals are excellent at removing and preventing the growth and spread of algae. So if you don’t feel like floating through a swamp, keep reading to learn about pool algae removal and prevention.

Types of Pool Algae

One size does not fit all when it comes to algae. There are three types of algae that can develop and wreak havoc in your pool. Identifying what sort of algae you have will help determine how hard it will be to eradicate.

Green Algae

Green algae is what most people imagine when they think of algae. It is the most common variety found in pools, and it is also the easiest algae to kill. However, green algae spreads rapidly, and can go from bad to worse overnight. Assessing the color of the algae in your pool will give you an idea of how difficult it will be to eliminate.

  • Light Green/Teal: At this stage, the algae is just beginning to bloom, and can be removed with relative ease.
  • Medium Green: This color indicates significant algae growth, and removal is more challenging.
  • Dark Green: If the algae progresses to this color, you have your work cut out for you! When algae progresses to this stage, it is much more challenging and time consuming to eliminate.

Yellow Algae

Also known as mustard algae, yellow algae is less common than its green cousin. Yellow algae is typically found in humid climates, and unfortunately, it is usually chlorine resistant. This form of algae often looks like dirt or sand sitting on the bottom of your pool. But don’t let that fool you. Ridding your pool of yellow algae is a bit more laborious than vacuuming up dirt. 

Black Algae

Black algae is not a fun, or easy pool dilemma to deal with. While black algae itself is not exactly harmful to swimmers, its presence indicates your pool is not doing its job regarding bacteria prevention. It is also very hard to get rid of, due to its deep roots and resistance to chlorine.

Materials Needed for Pool Algae Removal

test kit for pool algae removal

Gather up your supplies and get ready for some algae wrangling! Below are the tools and materials you will need to successfully rid your pool of its troublesome tenants.

How to Remove Pool Algae

Now that you have your supplies, and have identified what form of algae is in your pool, let’s dive into the steps for removing and preventing swimming pool algae.

1. Clean or Backwash Filter

This one is pretty self-explanatory. Before you add any chemicals, make sure your pool filter is clean, and clear of any debris.

2. Run Pump

Run your pool pump for about 36-48 hours during the algae treatment process.

3. Balance Water

water balance for pool algae removal

Since you will add strong chemicals into your pool to treat the algae, you need to make sure the other pool chemicals are adjusted accordingly.

  • pH: 7.8 or higher
  • Total Alkalinity: 80-100 ppm for cal-hypo shock
  • Cyanuric Acid: 25-75 ppm

4. Brush Pool

Brushing your entire pool prior to adding the chemicals is critical. The algae will loosen and break apart when you brush it, making it much more vulnerable to the algaecide and shock.

PRO TIP: Leave your brush in the pool during the treatment process. This will knock out any algae particles on the brush.

5. Add Algaecide

Choose the appropriate algaecide, depending on what type of algae is in your pool. If you prefer to use a metallic-free algaecide, opt for Algaecide 60 Plus. Distribute the algaecide around the entire perimeter of your pool, adding extra to problem areas.

6. Shock

In The Swim Super Pool Shock

After letting the algaecide settle for a few minutes, shock your pool with cal-hypo shock. We recommend using our Super Pool Shock, which contains 73% chlorine. Use a pound of shock for every 15,000 gallons of pool water. Depending on the severity of the algae, you will likely have to shock twice, if not three times.

Wait 12 hours between each shock treatment.  

7. Test Pool Water

Your pool just got quite a shock to the system, literally, so it’s important to check chemistry levels after algae treatment. Make sure pH, Total Alkalinity, chlorine, phosphates, and calcium hardness are all within their designated ranges.

8. Backwash or Clean Filter

Set your filter to backwash to thoroughly expel any contaminated water or algae particles. This is an important step, if you don’t flush out your pool filter, algae particles can creep their way back into your pool!

9. Vacuum and/or Add Clarifier

clarifier

If your pool water looks murky and dirty after all that time and effort defeating the algae, don’t worry. There are likely to be dead algae particles floating around in your pool after treatment.

Vacuum your pool to waste — or use a clarifier — to clean up, and clear up your pool. 

Steps for Preventing Algae

Now that you have seen the time and energy that goes into algae removal, follow these steps to prevent it in the first place.

  • Test and balance your pool water once a week. Additional testing is advised after heavy use. 
  • If your pool is used frequently, shock it at least once a week.
  • Clean or backwash your filter regularly. 
  • Run your pool pump for at least 10 hours per day to completely circulate the water.
  • Keep your phosphate levels below 100 ppb (parts per billion).

Don’t let algae-filled, swampy water ruin your pool time! We hope this comprehensive guide has helped you understand how to successfully tackle pool algae removal and prevention.

177 thoughts on “Pool Shock: Shocking for Algae Removal

  1. Living in Northern California we’ve been getting a lot of ash in the pool. We had it clearing up by brushing the sides/bottom and having the pump run 24/7. We also have a pool vacuum running. It had started to clear up, but now with more fires the ash has come back. What is the best way to help clear out the ash? Should I use an enzyme? Keep running the filter? Better vacuum? Additionally the plan is to clean the filter once the ash is done raining into the pool.

    • Davud, you poor people! Hang in there… Yes, keep brushing, running the cleaner and the filter. I would use one of Natural Chemistry’s combo chemicals, which combine clarifiers and enzymes and phosphate removers. Fire Ashes can contain phosphorous, nitrates, carbon and such. I would use Pool First Aid, or Pool Perfect + Phosfree, and also order the Filter Cleaning chemical. Also good to keep the pool deck clean as well, with a hose, blower or bucketing the deck with pool water, to keep it from blowing into the pool.

  2. We got a 12 x 36 intel above ground inflatable pool mostly for the kids but start to see the green stuff after the busy Holiday weekend, I got the one pound shock, but afraid to use the whole bag because i think they pool is to small for that amount or should I? Also is recommend it for those kind of pool?

    • Edward, yes you can use granular chlorine, but should pre-dissolve it in a bucket of water before adding. A 12′ has about 1500 gals, and the chlorine shock is usually 1 lb for 10,000 gallons, but for algae it is doubled or tripled for severe algae. So, you can add between 1/4 and 1/3 of a bag (4-5 oz) into the bucket of water and stir for about 1 minute, then pour into the pool. Be sure the pH level is on the low side, 7.2-ish, where chlorine is most potent.

  3. Hi,

    We have an intex pool. The pump stopped working almost a week ago. We have managed to get a new pump but in the mean time our pool has turned into a cloudy, sort of green murky mess. We live where we have gotten some ash from wild fires and I suspect some is in our pool. On the advice of the local public pool guy, I added a clarifier/algae combo and am running the new pump. After reading the blog, I think I have made a mistake but not sure. Should I shock the pool after the clarifier has a chance to do it’s thing?

    • Hi K, you can shock the pool, that is the best way to kill the algae. However if possible, I would drain and refill, unless that’s against the law in California 🙂

      • We are actually in CO so not quite as on fire as CA. Are you recommending to drain it because of the ash potential? I wanted to drain the pool when the pump broke but other people keep telling me that is not the way to go that I can salvage what is there. I guess the good news is that it looks slightly better this morning. Thank you so much for answering. Your blogs and q and a have been so helpful to this notice pool owner!

        • A little bit for the ash, but mostly because you said that you have a cloudy, green, murky mess – I think is how you described it. For an inground pool of 20K gallons I would not recommend such a method, but for a small Intex pool, it can be drained so quickly and easily (and cheaply), and because your filter will struglle with murky messes, it might be much cheaper and faster to drain and refill the pool.

  4. I was in a near death motorcycle wreck a few years ago & broke both legs (Femurs) as well as my pelvis, ribs, & too many to list. My Dr. said swimming would be great for me so I thought about getting a small model with constant current. Can you give me a “ballpark” price to install such a unit?

    • Robert, I can attest to the benefits of swimming myself. I broke my back on a snowboard nearly 30 years ago, and have suffered pain every since I started swimming, now in my fourth year. I swim VERY regularly, and it has helped me in so many ways, my hips and back feel brand new. Anyway, enough about me. I swim the local rec center and a local swim club in the summer, finding the social aspect motivating. But having your own backyard pool can be motivating as well! The swim spas tend to run around $12-$18K, with the large jet pump that you swim against. I would suggest that before ‘diving in’ to such a purchase, that you begin swimming at a local club, or in a friends pool, and then once you develop some comfort swimming, take a test swim (or two) in a swim spa or ‘endless pool’. They are nice, but a bit noisy, and may be expensive to heat in the winter, if you live in a cold climate.

  5. Tina Smith

    I added 7 lbs of powder shock to my really dark green pool! I jumped in vacuumed and brushed the walls and floor. I sure hope this helps. Test strips say everything is ok but obviously not if it’s green. When do I add pH or Alka..or cya to my pool? Also should I use algicide right after shocking?

    • Tina, chlorine is most effective at a lower pH level, so adjust the pH to be in the 7.2-7.6 range, and alkalinity should be 80-120 ppm. If the pool is still green, check pH and alkalinity, and shock again, keep adding until the water turns blue. If there is a lot of leaf debris in the pool, remove most of it first, so the chlorine attacks the algae and is not wasted attacking leaves. If you can drain and refill part of the pool quickly, that will help and also save money on shock, to dilute with fresh water. Algaecide is for prevention, don’t add right after shocking, the shock will destroy the algaecide and waste it. Wait a few days after shocking. Clarifier can help clear the water, as can running the filter non-stop. You may need to replace the filter media after the water clears (sand or cartridge), or use a Filter Cleaner.

  6. Dennis Elkin

    I have an 18″ above ground pool. I use plenty of shock and keep my Ph exactly where it should be. My test kits (I have 2 different types to confirm results) say my chlorine and Ph and alkalinity levels are perfect, but I continually get blooms of green algae growing on the vinyl surfaces of the pool. Just 2 days after shocking with over a lb. of chlorine, I get green algae. I’ve had similar results putting in 2 lbs of chlorine. What gives???

    • Hi Dennis, some pools have algae problems, some don’t. For those that do, it can be helpful to use a weekly dose of algaecide, to help control blooms. You also may consider replacing your filter media (sand or cartridge), if not done in years, since algae can harbor within. Another thought is that you may have high levels of phosphates, which is a tasty food for algae. There are many phosphate remover chemicals, such as PhosFree, recommended if levels are over 300 ppb. There also is a test strip for phosphates available. https://www.intheswim.com/browse?Ntt=phosphates

  7. Emily Leary

    How long after adding shock should you see a change? We have a 15’ x 48” intex pool that has developed Algae. I vacuumed and scrubbed the pool. I added shock, power power plus from Leslie, a 1/4 pound tonight but wanted to know should I see a difference tomorrow morning? Would covering the pool help? We are using the flippin frog for our chlorine but I’m thinking it may not be enough.

    • Emily, the dosage given on the label is really for clean/clear pools. For algae, double or triple the dose, depending on severity. Covering the pool can help. Using weekly algaecide treatment can also help and also having 20-50 ppm of cyanuric acid in the water can help to keep the sun from depleting your daily chlorine level.

  8. Nancy Fuentes

    Help!! I have an 18’ x 48” above ground pool. A few days ago a was surprised with a lime green pool. Had water tested and was told I just needed to shock it with 2 lbs of shock. Well I had already done that the previous day and nothing changed. So, I shocked it again with another 2 lbs. I brushed the bottom up all day and cleaned the filter about every hr. 24 hrs later (48+ since the first 2 lbs) after shocking and nothing has changed. What do I do now?

    • Hi Nancy, green is either going to be algae or copper ions. Copper will be clear green, algae is usually cloudy green. Copper is usually brilliant lime green, and algae is usually muted kelly green. If you think algae, keep adding shock until there is no green left. Could be 3-4 lbs per 10,000 gallons, or less. If you think copper, add a sequestering agent like our Stain Away chemical, to lock the metal in solution.

  9. Hi Davy,

    Your blog is so helpful and now I need help! We’ve been struggling to balance the chemicals in our Intex pool since the very beginning, and I discovered what I think is pool mold yesterday. Any advice about what to do to fix this problem? Thanks in advance!

    • There is something called white water mold, which produces what looks like white algae, on surfaces and floating/suspended. OR do you mean algae? In any case, to kill WWM or algae, put away the algaecide and pull out the shock chlorine. Lower the pH level before shocking, and put away any solar blanket to protect it. Shock, brush, filter, clarifier. Run the filter nearly non-stop if you can. Many Intex pool owners get into trouble by not running their tiny filter long enough each day. For chemistry, focus on a low pH, high chlorine, and then add recommended doses of algaecide and clarifier each week. If you get into big trouble, drain the pool or most of the pool, and start over.

  10. Amy Attree

    Are you saying only use chlorine, never algaecide?
    I have shocked my pool today and the chlorine levels are dropping quickly having given it another brush. The Ph is good. I was going to put algaecide in tomorrow. How long after putting it in the pool do I need to wait to add more chlorine? Thank you for your help. Amy

    • There are a few ways to approach it, one is to add algaecide and run the filter overnight, then shock the pool hard, which will unfortunately also destroy the algaecide. The algaecide weakens the outer protective coatings, and allows less chlorine to kill the algae, allows for faster and more complete kill. Second way is to just put away the algaecide until the pool clears, and then use it as an Algae-Stat, to control and suppress algae growth, before it gets started. Either way – Kill algae with chlorine, not with algaecide, despite the name, it’s more for control, when you want to correct an algae bloom, chlorine is the best algaecide! 20-30 PPM

      • Amy Attree

        Thank you for your comment, it’s was extremely helpful. Due to unavoidable circumstances my pool hasn’t been used in four years and the winter cover got damage and holy over that time so it was a swamp. I shock chlorined the pool to 30ppm and let it completely get used up and then added algaecide for 16 hours and the shocked it again at 30ppm. I brushed the walls and the floor and the green has completely gone.
        However it’s now a week later and the whole body of water is cloudy white. The Ph is 7.4 and I have kept the chlorine levels at 10ppm. Do you have any recommendations on how to make the water clear please?

        • Hi Amy, there are a lot of solids in the pool. I don’t remember if you can drain and refill some of the water, but if you could even replace a few thousand gallons, that would help speed up water clarity, lowering the water by backwashing, siphon or a small pump, and even refilling at the same time. Secondly is the filtration, run the pump 24/7 if you can bear to, and backwash only when the filter pressure rises. Use a pool Clarifier chemical once per week, adding the recommended label dosage and no more. If it still does not look at least somewhat better after a week, and certainly by two weeks, you may look at replacing the filter media (sand or cartridge), or using a product called a Slime Bag which attaches to the return fitting as a secondary filter, or using Alum (aluminum sulfate), 4 lbs per 10K gallons, to sink everything to the pool floor. You must be able to ‘vacuum to waste’, so you need a pole, vac hose and vac head, and also a way to eject the vacuumed water out of the filter system. If you have a multiport valve, just put it on waste. If not, you can install a 3-way valve or remove the cartridge and let the filter tank overflow, or by using a portable, deck-side pool pump to vacuum.

  11. Pool water is mint green. Did what pool place said. Added ph decrease, shock, etc, filter is changed everyday, we vacuum. Have tried clarifier. Water is clear, but not crystal
    blue. Please help!

    • Bright green water is usually algae, and the treatment is to keep adding shock until it turns a blue grey color… but sometimes, a bright green color is actually copper, especially if the water is clear, and the green is bright like a lime, not a darker kelly green color. You could add a Stain Away type of sequestering agent, to see if it will re-absorb the metals back into solution, assuming it is metals, and not algae.

  12. Hello! I have a 16×32 inground pool. It was a bit green when it was opened but is perfectly clear and looks great now. However, we can’t get a free chlorine reading. We had the same problem all summer last year. Pool looked spotless and clear but no free chlorine reading. All other chemicals are balanced. We have tried shocking with 4-5 bags of cal-hypo and running filter overnight – still no free chlorine reading the next morning. The local pool store couldn’t figure it out last summer and we aren’t having much luck yet this season. Any tips would be greatly appreciated!

    • Jen, some times this happens, and I can’t explain it – but some invisible force is eating all your chlorine. It may be nitrates or something. My cousins pool used to do this – most springs, until he shocked with 9 lbs of shock, that was his magic number, for a pool about the same size as yours..So, that’s my advice, shock with 9 lbs of shock to break through.

  13. Cathy Fazzary

    Hello, we recently opened my in ground pool but found the pump needed to be replaced. We put in the new pump but now it is not getting the pressure to push the water out of the jets & the suction under the skimmer box is not strong . It is strong when I put the plug in under the skimmer box & leave the one open in the skimmer box. The place where I go to get pool supplies said to put the hose in the skimmer box & put water in the lines to get the pump to prime. Not much luck yet! Getting frustrated, please help !!!

    • Hi Cathy, did you use a thread sealant on the pipe coming into the pump? Is the pump lid very tight? I’m thinking that maybe you have an air leak in front of the pump, which will slow the water flow. I’m assuming the new pump is the same make/model/size as the old pump? If not, it may be a lower flow pump, even if the hp is the same as the old one. It also could be that the impeller is clogged, from spring debris, common problem.

  14. Hi! I am new to opening a pool, I bought a house last year and the pool was already opened. When I had it opened this year the pool was a bright green. Was told to shock and use algeacide which I did. Pool is now a cloudy turquoise blue and have tried everything I have read to fix. I have been running the filters 24/7, cleaned the filters twice, used pool robot vacuum, brushed sides and bottom of pool (as much as I can without being able to see the bottom) and even put in some additional new water.The pool remains this cloudy turquoise cloor with foam on the top. When I’ve opened the filters to clean there is also a ton of foam inside. Not sure if this is because I put too much algeacide in at first pass? The other chemicals are all in line. I am desperate to figure out how to fix so if you have any additional suggestions please let me know! Thanks so much!

    • Foam is often a result of poor pH and alkalinity levels, combined with soft water. Check your pH, alkalinity and calcium hardness levels, to be sure you are in the good range. Some algaecides can cause foam, the ones labeled 10 or 50, aka Quats. Keep doing everything else, keep filtering. You may need to change the cartridges. have you tried a Clarifier? They can be very helpful.

  15. Geri L Cosgrove

    Is it better to fight a dark green pool with chemicals or just empty it and refill?

    • My rule of thumb is that if you can see the floor of the pool in the shallow end, you can bring it back with chemicals and filtering. However, if you have had algae in previous years, and you have not drained the pool in over 5 years, and if you are concerned about stains in the pool, I would drain and clean it, and also especially if the pool is on the small side, and/or if your pool filter is not the best or largest or most effective.

  16. We have been fighting white water mold in our 17000 gallon gunite pool installed not even a year ago. Today we added shock – 10 lbs of it! And also chlorine tabs in the skimmer. The person at the pool place told us we need to replace the sand in the filter, but it isn’t even a year old. Do you think the chemicals will do the job without the sand changing?

    • Hi Jessica, I would agree, that replacing the sand would be a good idea, as well as any soft or fabric materials used in the pool, that may have any trace of the spores. In addition, I would drain, pressure wash, bleach wash and refill the pool, if it was my pool 🙂 17000 gals is not much water, sure would be a lot easier. Sand is pretty cheap too.

  17. Sharon M Varin

    I have a 18foot round index pool and I’m just opening it up it was real dark green so I put3 lbs of shock in its starting to clear up slowly should I add algaecide and chlorine also to get it to clear up

    • Hi Sharon, did you use chlorine shock? That’s much better to kill algae. Algaecide, despite the name is not a very good algae killer, but is best for prevention. Plus, high levels of chlorine can destroy algaecide, so best to wait until chlorine level drops. Yes start adding chlorine, and two lbs of chlorine shock, until the water turns blue-grey. Run the filter 24/7 (it won’t blow up), and clean it as needed. Use a clarifier to help out the little filter. Replace the cartridge when the water clears with new.

  18. Cheryl Jorgensen

    I have a fiberglass pool that we had to replace just about all of the pool equipment on this year. The pool was super nasty green and we have an earth filter system. I have shocked the pool and it has turned a blue grayish color. I have back flushed many times because my filter pressure keeps rising and my flow slows down I am just not sure if I just need to keep doing this or if I am missing something else. I am afraid to leave the pool run to long because the pressure builds up so quickly.

    • Hi Cheryl, Is it a Hayward Perflex DE filter? With the “Fingers” instead of grids? First, are you using enough DE powder? When adding a Fresh charge, it is important to know that one pound of DE powder is not 16 oz, but 32 oz of dry measure, being that it is so fluffy and light. If that’s correct, then my next assumption would be that the filter grids or fingers need to be pulled out and cleaned thoroughly, and they likely are clogged with oils and/or scale. It’s a chore, but remove all of the little bolts, washers and nuts (put in a safe place!), and then hose clean. Then soak in a bucket with DE filter cleaner, or first soak in TSP solution to remove oils, and then soak in a mild 10:1 acid mixture to remove scale, and hose thoroughly with high pressure water after each soaking (soak for a few hours). Do it quickly, so the filter is not down for long, and once reassembled, try to run the filter 24/7 if possible, also ensuring that the pH is low and the chlorine is high.

  19. Christina Perez

    I’m in Southern California and I have a 22×52 above ground pool that i did not close for the winter and the wind took off with my cover so all kinds of everything ended up in the water. I purchased the deluxe opening kit and am a little confused when to put the algaecide in the water and the stain remover. The water right now is dark green. I’m still removing debris. The ph levels and alkaline levels are ready for me to add shock. I’m just lost on the other stuff. Please help

    • Hi Christina, since your pH and alkalinity are ok, yes go ahead and shock the pool first, after you get as much debris out of the pool as possible. You may need more shock than what comes in the opening kit, and should keep adding shock until the water turns blue-gray in color, with no green left. Then, check pH and chlorine level every 6-8 hours, to be sure pH is low and chlorine is high. If reverse, lower the pH and shock the pool again, especially if you see chlorine fall to near zero within 36 hours, that means you need more shock. Run the filter during this time, 24/7. The following day, add a dose of Clarifier to help the filter trap the small debris. Keep vacuuming and brushing and skimming to remove debris and dead algae. Once you see the water beginning to clear, and are done shocking, then you can add the Stain Away and the Algaecide, per label instructions. Since your filter is likely small, this might take a few weeks… keep at it, with low pH and high chlorine and constant filtering and cleaning… it will come back. If possible to do, replacing half the pool water with fresh water will make the process easier, faster, cheaper…

  20. We have a 40,000 gal pool- we have in the last 36 hours backwashed the pool 3 times, vacuumed the pool, brushed the pool multiple times and added 30lbs I’d shock and our pool is still green… it’s a lighter green and when I tested the water it shows a high level of chlorine in the water… but will not then the cloudy blue/gray!! Help!

    • Hi Sarah, 40K pool is a large one. I would recheck the pH level, make sure it’s still on the low side 7.2-ish, where chlorine is more potent. Monitor the chlorine level today, and if it drops down below 3-4 ppm, add more shock. If there is debris (leaves/sticks) in the pool, that will absorb or consume some of the chlorine. So, keep the pH low, the chlorine high and keep filtering! A Clarifier would help the sand filter restore water clarity faster. This could take another few days, and perhaps more shock, esp. if it does retain the green color. You know that at least you’ve killed all the algae, when the color turns from green to blue-gray.

  21. Help! I just moved into a house that has on the ocean with an in ground pool. This is my first cleaning of the pool. It was green and now the algae is floating on the top of the clear water. Should I just run the filter?

    • Hi, yes run the filter 24/7 while treating algae, backwash as needed, and be sure the filter is running properly, with good pressure and flow. In addition to near constant circulation and filtration, you also need good sanitation. Be sure that the chlorine level remains at 3 ppm or higher, and that the pH level remains at 7.6 or lower, and the algae will go away. CLeaning the pool is also helpful, if there are leaves and such. Use a good brush to remove algae stuck on the walls and floor.

  22. tina oast

    are the closing chemicals and the opening chemicals the same? Can I use the closing kit to reopen in the spring

    • Hi Tina, they are similar, except that our opening kits have chlorine shock and closing kits have non-chlorine shock. Algaecide for closing kits is a different formula, but can still be used any time of year. So yes, if you have a closing kit that went unused, you can use it in spring! Thanks for asking.

  23. Hi Davy,
    We purchased our house 3 years ago (w/23,000 gal pool) and have been maintaining the pool for the last two yrs. Have been dealing with black algae about a yr. Switched pool chem stores after liquid chlor/acid and black algaecide were unsuccessful. Switched to Leslie’s and it’s gotten pretty expensive to maintain proper balance using power powder plus, conditioner, no phos, perfect weekly and black algaecide. (lot’s of brushing) Algae has spread and I’m exhausted trying to keep up. Thinking of going back to original with liquid chlorine and acid… Thinking it was a matter of not shocking enough and keeping the chlorine levels high enough. We have an intellaflo pump and am using the old pool service program that they input along with a several “quick clean” cycles throughout the day. (Need to learn how manually run it for the longer duration) Any more ideas would be much appreciated!! Thanks!!

    • Hi Nancy, if you really want some relief with black algae, drain the pool, then pressure wash the pool to remove the algae heads, then quickly chlorine wash the pool. The next day rinse well, pump it out, and then acid wash the pool. Then refill the pool. Replace the filter media (sand, cartridges or DE grids), and any soft fabrics like pool cleaner debris bags, or skim nets. Balance the water, and keep the chlorine level high (3-5 ppm), with a good pH (7.2-7.4), and use a weekly algaecide. That is the only real method, chemicals won’t work very well, unless you are in the pool daily, scraping off every single algae head, and even then it can be difficult to control. The method I describe is best for black algae, but even it may only last a few years, at which point the process can be repeated. The only sure cure I know of is to replaster the pool, along with new filter media. Also replace swim suits, which may have black algae spores in the fabric.

  24. Hi, when you say the water should turn gray/blue-ish color, do you right when adding shock? Or like within hours/days?
    Thank you

    • Hi, I mean right away, within 5-10 minutes. If a green pool does not turn bluish-gray, immediately after shocking – needs mo’ chlorine! Keep adding. Algae can require 2 – 9 lbs per 10K gallons, depending on severity. Average algae shock dose is 3-4 lbs shock per 10K gals. Make sure pH is low, 7.2-ish, where chlorine is most potent.

  25. Samantha Burnette

    Hi I have a pool that is around or a little over 17000 gallon above ground pool. After a day or two of the pump being off and us not knowing it started to turn light and medium green so we tested it and it said on low. I didn’t know at the time I needed to shock it first and then test the ph. How can I get our pool back to being clear. Please help us

    • Hi Sam, yes – check the pH and adjust to the low-side or around 7.2, where chlorine is more potent. Shock the pool with 3-4 lbs of Pool Shock (or until it turns a blue/grey color), and run the filter 24/7 until water clears. Using a Clarifier can help, but wait a day for the chlorine level to subside. Check the chemistry 2x per day, and keep pH low and chlorine high, and keep running the filter… should clear up in 3-5 days.

  26. Hello Gary,

    we recently installed a 24 foot above ground pool. We are on well water so it is taking alot longer to fill up the pool, because we can only do alittle at a time. We were away for a week, while we were gone alot of rain came in. The water was cloudy and had large brown areas that cover most of the pool and lots of tad poles. Instead of waiting until the pool was full and letting the stuff to continue to grow. I added a bag of shock to the pool. its about 1/3 full. I dissolved it before pouring it into the pool. The pool began clearing up within the hour. My concern is will that bleach my liner and is there something i can put in there to help dilute the shock

    • Hi Jess, likely no problem adding the shock, probably did not bleach the vinyl, because of the heavy fur-coat of algae! 🙂 Should be OK – but do try to fill faster, and keep it chlorinated, brushed and skimmed every day. If you have a pool cover or tarp to cover the pool while it is sunny, that can help keep the algae growth minimized. Add enough shock (diluted first in a bucket of water), to turn the water a blue/grey color, then add a little bit more, about 1/2 bag, every few days, or when chlorine drops to zero. Add a chlorine floater with chlorine tablets, to release chlorine slowly thru-out the day.

  27. Anna Newcomb

    My pool was green so I put shock in it now it’s a cloudy blue, i’m planning on putting actual bleach in it, and I shocked it yesterday.. so do you know how much bleach I can put in my pool
    it’s 16ft , and 5,246 gallons??

    • Hi Anna, for regular bleach (6%), use 1-gal (4-Qts) to reach about 11 ppm. That should be sufficient for a regular shocking. For severe algae, with little visibility, 2 or even 3 gallons could be used. Be sure the pH is around 7.2, where the chlorine is most potent.

  28. My pool was closed for 2 years. It’s gone from dark/black green to lighter and then started back going dark again. My numbers on filter are not real high not at 20 but I have backed wash just in case. I feel like I should just keep adding liquid shock and do have added chlorine into my automatic chlorinater. Is this okay

    • Hi Donna, thanks – good question. First, keep the pH level low, 7.0 – 7.2, where chlorine is most potent. Secondly, run the filter non-stop, or nearly 24/7. Third, shock the pool very hard, to reach 30 ppm, which is normally achieved with a triple shock, but in your case, maybe 4x is needed, which is 4 lbs of Pool Shock per 10,000 gals, 4-gals of liquid shock per 10K gals. And tablets in the chlorinator, yes. Vacuum, brush, skim to keep the pool clean. Keep running the filter. A Pool Clarifier can be used to help the filter…

  29. I am newbie and have a newly installed above ground pool and finally got the electrical installed for the pump. My question is, what chemicals do I use first? Thank you in advance

    • First balance the water, especially the pH and alkalinity, then shock the pool to kill anything that started growing in this summer heat. Run the filter non-stop for a few days to catch up on that, and then you can use a timer to reduce run-time at night. The next day, start using tablets, in a floater or feeder, to build your daily chlorine level, very important to be constant and consistent, 24/7 – the water must have a measurable reading of 1 to 2 ppm of Free Chlorine (all the time), as measured by your test kit or test strips. You also may need to add a few lbs of cyanuric acid, aka Stabilizer, to help maintain a chlorine reading during hot and sunny days. If the filter is small and water looks dull, use a Clarifier to help, and if you notice algae, kill it with a shock treatment and begin to use a weekly dose of algaecide. Shock the pool every 2-3 weeks, to disinfect and sanitize the water, or to remove chloramines, or for algae or cloudy water, or suspected bacterial infection. Have Fun!

  30. Michelle Robinson

    How do I get areas of algae off the bottom of my pool. I have shocked, brushed,vacuumed to waste, the bottom stays clear for a little while then small areas of algae return especially in the shallow end.

    • Hi Michelle, first make sure water is balanced, and pH is kept on the low end of the scale, 7.2 – 7.4. Secondly, make sure that a consistent and constant level of chlorine ALWAYS exists in the pool water, 24/7 – a level of 1.5-2.0 ppm. Third, make sure the filter is running long enough each day, which may need to be 24/7 depending on the filter effectiveness. Fourth, consider changing the filter media (new sand or new cartridges), which can trap algae. Fifth, begin using an algaecide weekly, a good algaecide with “60” in the name, or a copper algaecide (don’t buy the cheap stuff). Finally, brush the pool well, twice per week. Good luck!

  31. This is great information! I’m wondering if it will help our situation. I have a 15,000 gallon Gunite pool that is one year old and has some staining on the side walls. A chlorine tablet placed on the stain will remove it, but I’m not sure how to address the entire pool. Not sure what chemicals are safe for Gunite and what the dosage should be. Do you have any advice? Thanks!

    • Hi, granular chlorine (pool shock) is a great stain remover for gunite pools, removes most organic stains instantly. Just sprinkle some of the granular over the area, let it sit for a 30-60 seconds then brush away with your pool brush. Since your stains are on the walls, that becomes more difficult – but if you use 3 lbs of shock in the pool, it should lighten the wall stain. Another option is to lower the water level down below the wall stains, and pour a light muriatic acid mixture from a thin necked flower watering can, over a wet wall surface, to ‘acid-wash’ off the stains.

  32. I have done a quadruple shock on my pool in the last 24 hours. I have vacuumed skimmed and brushed but we have a lot of trees around the yard. I checked the pool levels and the levels are pretty good, although chlorine is a little low.The pool is about 30,000 gallons but it still looks cloudy. I can see the bottom, but the water is like a cloudy pale blueish gray. What else can I do so I can finally use my pool? I think there is some algae in there and I stirred it up some when I brushed again. I just want to use my pool! Please help!

    • Hi Amy, keep filtering the pool, 24/7 if possible. Your filter sand or cartridge may be tired and needing replacement – fine for normal duty, but struggling with fine particles. Using a Clarifier can help at this stage, to coagulate smaller particles into more easily filtered clumps. Keep the pH low and the chlorine level high. If you have a multiport valve, you can vacuum the pool To Waste… if not, brush the pool daily, and keep the surface skimmed.

  33. Gary Bradley

    I have a 15,000gal tiled pool in Mexico and am having trouble getting rid of black algae. The water clarity is very good. I drained the pool in January and wire brushed every single grout line. Unfortunately the algae returned very quickly after just a month or so. I have added an algicide which seems to be softening up the algae for easier brushing, and after a day I shocked it. It is looking much better, but is a 30 hour procedure. The pool is also surrounded on 1 side by a large jungle like wall of vegetation as well as a 20’ high California style waterfall. Is it worth using a phosphate remover like pl-10000 or is replacing the water (free) a better option? I removed a salt generator last year and use chlorine pucks instead. Ph is stable but it’s difficult to maintain a good chlorine level. What can you recommend for these conditions to control the black algae?

    • Hi Gary, I would try a phosphate remover, or at least test for phosphates, with phosphate test strips. Black algae is also known to become trapped inside of pool filters, so changing filter sand is a good idea when treating, and also replacing any soft materials used around the pool like foam noodles or mesh floats. Also check the cyanuric acid level, to help maintain chlorine level

  34. Marcella

    I have a 17,500 gallon size pool. Our pool is a dark green after 2 days of shock and a dose of algaecide. Our chlorine level is at a 15, extremely high, but everything tests regular. What can I do to make my pool blue and clear again?

    • Marcella, run the pool filter 24/7, and if it’s not improving water quality, replace the filter media (sand or cartridge). If the pool is still dark green, you need more chlorine, 30 ppm is necessary to kill the algae in most cases. Keep adding until the pool turns a blue/grey color. And also keep the pH level low, very important, in the 7.2-ish range, which makes chlorine more potent.

  35. Robert G Willis

    I have white water mold. I also have a bump regeneration de filter. I followed direction about bags of shock in my 15000 gallon bag pool. But the filter pressure rises 6 to 8 in a matter of a few hours. How do I go about getting rid of wwm with a de filter with the bump regeneration system?

  36. Jennifer Carver

    I just shocked my 15 ft pool and 24 hrs later everything is low. What do I do next? It’s a light blue cloudy color. Like blue Kool aid. This is my first pool and the first time I have shocked it. Please help!!!

    • Hi Jennifer, sounds normal – keep filtering the water – nearly 24/7, and keep the chlorine level up around 2 or 3 ppm. Some clarifier can be used if it won’t clear up in another day

    • Lawrence Hopper

      Hi Jennifer,
      If your pool hasn’t cleared up. If my pool has a lot of algae. The next day after I shock it. I add Flocculant ( Drop Out ) and run the pump for a couple of hours. Then shut the pump off and wait 12 to 24 hours. All the dead algae will fall to the bottom and can be vacuumed to waste. Or vacuumed and sprayed out into your yard. Your filter cant catch all of the dead algae and it will blow through the filter and back into your pool. so it has to be vacuumed to waste. clarifier takes particles that are to small for your filter to grab and clumps them together so the filter can get them. Flocculant attaches to particles and makes them heavier so they will fall to the bottom of the pool.

  37. Scott Schroeder

    Hi,I am totally frustrated! Changed my 30,000 gallon pool to salt and cartridge filter. The pool has been green for 2 weeks. Last night I put in 5 lbs of stabalizer and 6 gallons of liquid shock. 24 hours later and my stabalizer is 0 and my fC is 0 and TC is 1. How can that be? Do I need to get my cuuranic acid to 30-50 ppm before shocking?

    • Hi, how’s the pH level? Salt tends to raise pool ph, and as pH rises, chlorine becomes lazy and sluggish. Cyanuric acid can take a few days to begin to register with a test strip or kit. If the pool is still green, adjust pH to 7.2-ish, and shock with another 6 gallons of liquid or 6 lbs of granular. The liquid you are using , make sure it is fairly fresh, NaOCl loses potency within 6-12 months, has a short shelf life.

      • Scott Schroeder

        Shocked with 73% cal-hypo, 12 hours later and the algae is finally gone! Just added muriatic acid, PH is way high. Hopefully my kids can swim in a few days. Thank you for your advice!

  38. Hi- we opened our pool for the summer about a week ago. It was clear then turned green. We took a sample of water to the pool store and they said to do this 3 day program with algaecide destroyer and shock. So we did. The water is a light green, bluish tint now but the problem is the white layer or foam stuff on top of the water now and I can’t get rid of it. As soon as pump comes on it gets bad. I can stand and scoop it out all day long and it never goes away. We even changed the sand in our filter. We have an 18’ above ground pool that is 10,000 gal. We bought it at The Great Escape

    • HI Rebecca, the foam may be from an algaecide, certain types do foam – it should subside in a week or so…

  39. I have been trying to open my pool for summer since Sunday. It is now Friday morning 😩. I have shocked and backwashed for several days. It is blue but still very cloudy and has a little white film in some areas. Any suggestions? I would love for it to be ready by tomorrow.

    • Hi Kendra, clean and blue water is a combination of filtration, circulation, sanitation, water balance, and nice weather helps. Most important perhaps is the filter, to remove the particles that make water cloudy. Small, undersized or underperforming filters struggle with cloudy water. Filters with old filter media (sand or cartridges) struggle. Run the filter 24/7 (it won’t blow-up!), and clean when the pressure rise 5-10 psi, or the water flow noticeably slows down. You may need a filter media change, or using a Filter Cleaner can help. Filter Aids can also help, like a cup of Alum or DE Powder or Jacks Filter Fiber into a sand filter. Or a product like the Slime Bag, which attaches to the return line to act like a second filter. Using a Clarifier can also help coagulate suspended particles into larger, more easily filtered clumps.

      Aside from filtration, it is also important to have balanced pH, alkalinity and calcium hardness. Also be sure that you have a constant and consistent chlorine reading adn the stabilizer level is 20-50 ppm, to protect from the sun (too low or too high (100 ppm+) can be a problem). Keep the chlorine level high (and the pH level low) when trying to clear a cloudy pool. Very high Alkalinity or Calcium Hardness levels can contribute to cloudy water.

      Aside from water chemistry, keep the pool clean by vacuuming, brushing and skimming the surface every day, this also helps to clear a cloudy pool. It can sometimes take 7-10 days to clear completely. Be vigilant, because it’s easy to fall back a few steps and get cloudier. For more cloudy water pool treatment tips, see these 10 blog posts.

  40. Lorraine

    Hi I shocked my pool last evening, it was a dark green colour, how long do I need to wait to see any effect as this morning there is no change. My ph was low before I added the shock.

    • Hi Lorraine, so the algae just laughed at you, huh? That just means that you need more shock! The level of solids and algae in the pool is greater than the amount of chlorine used, so repeat, but this time add more. The package dosage for shock is really for clean and clear water – 1 lb per 10,000 gals won’t do much for a heavy algae bloom like you see during spring openings, or dark green, as you say. A triple shock, or sometimes 4x dose is needed – just keep adding until it turns blue, before your eyes, within minutes. You won’t have to wait long. If it’s still green, add more – keep adding until the water turns a blue-grey color…

  41. Charles Leahy

    My pool is green and I have put 16 gallons of shock in my 33 foot round above ground pool and it is still green. What do I do.

    • Be sure that the pH level is low, or aroudn 7.2, which makes chlorine more effective. You also need good circulation and filtration, to clear the water. If still green, that usually means that the algae is still viable, and the chlorine demand is higher than what you have added. The liquid chlorine may have lost a lot of potency, it has a short shelf life.

  42. My on top ground pool is rectangular and is 18′ x 9′ x 48′. How do I figure how much water does my pool hold? Right now is green trying to figure the amount of shock to put in it.

    • Hi Cindy, to figure gallons in a pool, the formula is L x W x Avg. (actual water) Depth x 7.5 = Gallons. so for your pool is 18 x 9 x 3.5 x 7.5 = 4252.5 gallons. (give or take a few). I would first adjust pH to the low side of the scale (around 7.2), then add 2 lbs of pool shock, pre-dissolved in a 5-gal bucket of clean water.

  43. We have a 38000 ganite pool. It was dark green. We put in 20 pounds of hypocal let it filter 24 hours then added two yellow gone and a bottle of Algecide for all types. Checked water today very light green cloudy milky looking however out chlorine level is now back to zero. Cya level was now low. We added stabilizer waiting for it to come back up. Should we wait for the cya to come back up and if so which to add next more hypo cal shock or first add the drop out?

    • You may need another shocking yes – I would shock first, with about 7 or 8 lbs of pool shock, with a suitably low pH (around 7.2 or 7.3), and run the filter non-stop. After a few days if needed, use the Drop Out (flocculent) chemical…

  44. Running my filtration system for the 24 hours during the shock process is causing pressure to build up to where I would normally backwash and rinse the filter. My pool is dark green so the amount of funk it’s picking up is no surprise that it’s impacting filter performance. Is it ok to do this during the shock process or should I wait until the 24 hours has passed and then frequently backwash as it filters the less green or cloudy water?

    • Hi Tara, if a sand filer is clogging up too fast – you can place the multiport valve on the recirculate position, to circulate the water, but not filter it. You may need new sand after the water clears (or before), or at least a sand filter cleaner.

  45. David Cowell

    What is best to reduce the ph levels before shocking as mine is between 8.2 -9.0 after shocking a few days ago thanks

    • Hi David, to lower pH you add an Acid to the pool, either liquid muriatic acid, or dry acid, sodium bisulfate, aka pH Decreaser. Closely related to pH is alkalinity, which is best in the 80 ppm to 120 ppm range. If too high, it can make it hard for a pH adjustment to ‘stick’, allowing the pH to rise quickly again. To lower your pH from 9.0 to 7.4, add 3 lbs of dry acid, or 1/2 gal of acid, per 10,000 gallons of pool water.

  46. Charlie Barr

    my pool was dark green I have shock it with liquid shock and algae stuff plus chlorine tablets it light green now and more shock

    • Hi Charlie, if it is still green after shocking, I would check the pH to make sure it is between 7.5 and 7.5, and then shock it again. The general rule of thumb is to keep adding shock until the water turns blue-ish, or blue-grey, which happens before your eyes, within minutes. Or
      1 lb shock per 10K gals for clear water,
      2 lbs shock per 10K gals for light green,
      3 lbs shock per 10K gals for medium green,
      4 lbs (or more) shock per 10K gals for dark green

  47. Hi , I have a 24 ft round above ground pool, this winter my cove3 fell in the pool, my water is black , what can I do to get my pool ready before summer starts ?

    • Hi Sandy, I would first drain half the pool and refill, if possible. And then repeat, if possible. OR drain the entire pool and refill. Otherwise, balance the pH, alkalinity levels and shock it hard with 4 lbs of shock per 10,000 gals, more or less, until the water turns a blue/grey color. Then run the filter 24/7, cleaning as needed, and keeping the chlorine level high and the pH level low. add a clarifier to help the filter. Re-treat with shock as needed, and new filter cartridge or sand may be needed after clean-up. Depending on the performance of your filter, it could take 5-15 days to clear up.

  48. Lonita Williams

    I am new to cleaning my pool my husband did it but he has passed away suddenly. My pool was dark green I shocked it and have the setting on circulate its now a cloudy blue (looks much better) i backwashed for about 5 min i guess and I put it back on circulate. I notice your blog keeps saying filter. Do i need to put it on filter setting. Also my label has faded all I can see is backwash filter and circulate can you tell me what the other settings are?

    • Hi Lonita, my condolences! The Filter position is where the valve should be 99.9% of the time. Recirucate just returns the water to the pool, unfiltered. The Filter position will be opposite Backwash, or 180 degrees. Recirculate is opposite Waste and Rinse is opposite Closed. Multiport Valve Settings Demystified:

  49. Jan Goodloe

    I just added algaecide after brushing down the pool. I didn’t realize I should have shocked it instead. Should I shock after 24 hours and vacuuming?

  50. Daniel Hightower

    I have a 15k in ground pool. Live in area of Tx temps now running 80 degrees during day and I a getting the pool ready for summer. It has stayed. clean most of winter I hit with shock last week, now chlorine at 3 ppm. Hit it with 60 algecide (16 oz). put new tabs in skimmer. Am I good or do I need to hit it with more shock next week just to make sure?

    • Hi Daniel, sounds like a good start! No need to shock again so soon perhaps, if everything else is in-line and working well.

  51. I found your page by searching for algaecide, but it looks like I should just shock rather than using algaecide? I began shocking yesterday, so it looks like the time for algaecide is past. From what I’ve read above, algaecide, wait, then shock?

    Our water is very clear, but it has a medium light green tint.

    • Hi Mark; Great question, thank you. For killing visible algae, shocking the pool with chlorine is best. For preventing future algae outbreaks, algaecide is used. Algaecide will help remove the protective layers of algae, to allow your chlorine to easily penetrate the cell. A good algaecide will kill small algae blooms, or pools with a light green tint, but it is important to know that in most cases, shocking the pool will destroy or damage or deactivate the algaecide. So the best process for algae is to 1) balance pH/alk/calcium/cyanuric, and 2) shock pool with 2-4 lbs of shock per 10K gals, depending on visibility and 3) Brush, Vacuum, Filter. After the chlorine level comes down in a few days, add a good dosage of algaecide, to help prevent it from returning so easily

  52. matt benoit

    Hi, we had a new kayak pool put in last month and it came with a frogger system autocholorinator. The installers suggested to leave it at one of the lower settings, but I kept getting low chlorine levels so I have been shocking on a weekly basis. I turned the clorinator up a level but I’m still getting cloudy water and noticing very small sections of yellow algae on the bottom corner… should I add a floating chlorine skimmer to help the frogger system out? I’m pretty anal about cleaning the pool, and it gets vacuumed once a week. I feel like with all I’m doing, I shouldn’t be getting any algae… any suggestions?

    • The frogger system should manage most sanitation if operating correctly. Assuming it is delivering .5-.7 ppm of chlorine and the mineral cartridge is ‘mineralizing’… then I wonder how’s the filtration and water balance? When it’s hot (like in august), you need much more filtration than during cooler months. Usually Kayak pool filters are on the small side, so I’m suggesting that you may need to run the filter longer, 12 hrs+ each day. Also be sure that pH is nice and low 7.2 – 7.4, to make the chlorine more active, and when shocking the pool for algae or cloudy water, give it a double dose 2-3 lbs per 10K gals.

  53. Nancye Hoffman

    If my pool looks good and everything is at the ideal level on my dip stick tester strips (total chlorine, free chlorine, stabilizer, pH, alkalinity, & hardness) should I still shock it?

    • Davy Merino

      Hi Nancy, great question, thank you! The short answer is no, no need to shock the pool unless you are seeing 1) algae, 2) cloudy water 3) chloramines (combined chlorine) or 4) if the equipment (pump or filter) is inoperable or if chlorine level drops to zero, or 5) after heavy use of the pool (big party), or 6) heavy rains – or if you suspect some other sort of contamination. Weekly shocking is overkill in most cases. Monthly may not be enough though… definitely depends on the pool, how clean it is, how often it is used, and the effective level of filtration, circulation and sanitation practices.

  54. Stephanie Cummings

    My pool water is still clear but visable algae on the bottom corners and the bottom side. I brushed it all away and dumped a 1/2 gallon of liquid super shock. My clorine levels all summer have been steady along with PH and alkalinity. We where running the pool 6 hours a day but bumped it up to 8 hours. It’s a little over 10,000 gallons. Why question is I guess since my water is clear what should I do next?

    • Davy Merino

      Hi Stephanie, running the filter even longer each day would help, maybe 12 hours daily, won’t cost but $1 per day more or less. Second, if the pH is high – algae prefers that, and it makes your chlorine lazy, so running a lower pH 7.2-7.4 can help thwart algae. Third, keep brushing daily if you can, it’s great exercise! Fourth, either use an algaecide, initial dose and maintenance dose -OR- shock the pool every 2 weeks, with 2 lbs of granular shock, or 2 gallons of liquid pool shock, per 10K gals (your pool size), to keep the algae under control. Fifth – if your filter media (sand or cartridge) is old and gone thru many algae battles, it may be time to replace.

  55. Nathan Burgess

    Hi, I have a 450 000 l training pool, I have just used algacide and the pool has gone from green to blue with all the algae on the floor, however my Chlorine levels are below 0.5, how soon after an algaecide can I start adding large amounts of Chlorine to being the Chlorine level up to 2.5

    • Hi Nathan, since the pool color has returned to blue, I would say go ahead and raise the chlorine level now – fast! (or it may turn green again)

  56. I have a 4400 gallon above ground pool. I’m noticing a light film forming on the surface, which I’ll assuming is algae. The recent cya level was 70 ppm. I’ve decided to add hth super pool shock as to not increase the cya level. The directions say the to add the 1lb bag for 13500 gal. Do I just add half the bag and store the rest?

    • Hi Kris, algae does not normally float on the surface, might be something else, some wind blown dust or pollen perhaps. But to answer the question, yes you can store the remaining shock, but very carefully! Fold it over and clip it tightly shut with a plastic clip, and then place in a plastic container, to keep out moisture, dirt and bugs, and protect against spills. half open bags of shock can be dangerous if not carefully stored. Good question, thanks!

  57. Megan Kelley

    Hello my pool is 1,500 gallons how much shock would I put in it?

    • Hi Meghan, somewhere between 1/5 and 1/2 of a bag – depending on the severity of the algae or condition you have. If you are just superchlorinating, a regular raising of the chlorine to 10 ppm, use about 3 or 4 oz of Cal Hypo shock, but if you have a full blown algae attack, use 8 or 10 oz, or until the water turns blue-ish. A low pH is best for greatest chlorine shock potency. Check the label, all pool shock will have dosage instructions, usually based on 10000 gallons, so you just do the math. I also like to use poolcalculator.com to calculate precise chemical dose amounts, for shock and everything else.

  58. I am using an algaecide as a preventive measure in my pool and added ~12 oz to my 33k gallon pool. I plan to shock tonight. Is 24 hours enough time to where I won’t cause any chemical reactions?

    • Hi Charles, yes 24 hours is long enough for the algaecide to have done most of its job, and can now be put to bed. Meaning that, shocking the pool may likely destroy or disrupt the algaecide. No chemical reaction really, other than high levels of chlorine tend to break apart the polymer chains in polymer and poly-quat algaecides, depending on the level of each in the water at the time.

  59. I CAN’T GET RID OF MY ALGAE. THE POOL SIZE IS 16X32. THE WATER IS CLEAR BUT THE SIDES OF THE POOL GET GREEN ALGAE IN SPOTS. AFTER I BRUSH THE POOL AND VACCUM UP THE DEAD ALGAE( GRAY AND WISPY) I SHOCK THE POOL. THE NEXT DAY WHEN I TEST THE WATER THE FREE CHLORINE DOES NOT SHOW UP ON THE TEST STRIP. I HAVE SANITIZED THE POOL BUT IT DID NOT HELP. HELP

    • Hi Henry – when that happens (the day after shocking the pool, the chlorine is zero) that means that there is something in the water consuming the chlorine, just as fast as you can add it. You may have a phosphate contamination, which can be tested with phosphate test strips, and removed with phosphate remover – or, you may need to just shock the pool with a triple shock, adding 3 lbs of shock per 10000 gallons, to reach that breakpoint threshold, where the water is completely sanitized or disinfected. Hit it Hard! Also consider replacing the filter media (sand or cartridge), or at least using a Filter Cleaner, to remove the dead remnants of algae buried deep in the filter, which can provide food for new algae growth.

  60. Kristen Brown

    I have a small pool, about 3500 gallons. We have been having an issue with algae due to excessive heat in our area. We are in a heat wave and it won’t get below 110 for the next month or so. We shocked and then used the vacuum and added a clarifier. All the algae just ended up settling at the bottom. I just bought more shock. The chlorine levels aren’t even registering for my test kit even though we use 1-2 tablets a week. Our PH is around 7.8 so I figured I better skip next week on my PH tablet. We scrubbed and netted the pool and just added 9 ounces of shock which is double what the instructions say for my pool size. It’s between light and medium green. Is it a good idea to just ignore the instructions and use more?

    • Hi Kristen, when shocking to remove algae, keep adding until you see the water turn a blue-grey color, within minutes. If it still looks green, add more. First lower the pH level a bit, to 7.2-ish, where the chlorine will be more potent. Generally speaking, package directions are good for isolated algae, in one or two spots around the pool. Do a double shock for widespread algae, and a triple shock for pools where visibility is poor (moderate to severe algae) – and sometimes even 4x or 5x label dose is needed for dark green pools.

      You didn’t mention filtration, but your filter plays a large role in algae control. If not already, run it nearly 24/7, and look for ways to improve pool filtration . A new filter cartridge or filter sand, or using a Filter Aid or Clarifiers can also be helpful, and often necessary.

      • Kristen Brown

        Thank you! Our pool is now blue/grey. We are using the filter that came with the pool and replacing the cartridges every other week. My chlorine levels are super high now. Just waiting for them to come down so I can add some acid and then the clarifier. Where should the chlorine levels be before I can add my other chemicals?

        • Kristen, no need to wait to add the acid, if you need to lower the pH, do it sooner rather than later. For clarifier, I think that 24-48 hrs after shocking would be sufficient, no need to wait any longer, even if the chlorine reading is still very high, which may contradict an earlier statement of waiting until chlorine is below 5 ppm, but it’s not really about the cl level, but more about letting the chlorine do its work without coagulation processes going on. Good luck!

  61. My ph is 6:56-6:57. My pool is light green cloudy water after i added 3 lb og super shock and algaecide, ruuning pump but not 24 hrs as it is noisy. Now how i raise ph to 7.2 Is it something else i need to meadsure or add? Pls help, i really appreciate. Water has little particles

    • Hi Fifi, pH of 6.5 is in the acidic range, and over long periods of time this can damage pool surfaces. To raise pH, just add a BASE, Soda Ash, aka pool pH Increaser. Pool shock works best at a lower pH level. If the pool is still green, you may need to shock again, until it turns a blue-ish color, to kill the algae present. Oh, and next time don’t add shock and algaecide at the same time, in most cases the shock will deactivate and destroy the algaecide, which is best used for prevention and control of algae, despite the name algae-cide. Use Shock to Kill algae, and Algaecide to prevent it from coming back… Using a Pool Clarifier can help your filter trap the small particles, added a day or two after shocking the pool, or after chlorine level has returned below 5 ppm.

  62. ivonne garcia

    The ph is 7.2 but the alkalinity is high at 180 and my water is a little cloudy what can I do I started adding dry acid it’s a 4440 gallon pool.

    • Hi Ivonne – well, with such a difference in pH and alkalinity, you have a week or two of adjustments ahead of you. Raise the pH, lower the alkalinity, raise the ph, lower the alkalinity, back and forth in this see-saw method until both come into proper range. Or, you could drain the pool, fully or mostly, and refill with fresh water – tested first to be sure that your tap water has better pH/alk levels – or some combination of both – draining and adjustments. Good luck!

  63. We bought a house with a pool that has not been kept up with. It was a nasty swamp green when we moved in and we tried to find someone to clean it. No help so far. We have gotten our water tested and spent so much money trying to get it clear so we can vacuum it but the algae keeps coming back. It’s a light green cloudy color now.

    • Hi Meka, Is it possible to drain it and refill with fresh water? That would be make your summer so much easier! Even if you just replaced half the water… old pool water that sat stagnant for long periods of time is a lot of trouble. If not possible, test for phosphates, and treat with a phosphate remover, and consider replacing the filter media (sand or cartridges).

  64. We just bought a house with a pool that has not been kept up with. It was pretty green when we moved in and we went ahead and hired someone to help us get it under control. After we got the water cleared, we noticed that the walls had black algae. Our pool guy added 50 pounds of shock two weeks ago and the chlorine levels are still skyhigh. When I stopped by the pool store today, they thought that was very excessive. Is this normal practice and is there a way for us to lower the chlorine levels? On a sidenote, the black algae is gone! 🙂

    • 50 lbs of shock is a LOT – but it cured the problem, so no worries. Chlorine levels will naturally lower over time. There is a product Chlorine Neutralizer that can be used (sodium thiosulfate), or you can just let it come down naturally. Shouldn’t be too much longer.

  65. Why use a hypocal shock with a higher minimum available chlorine %? I typically use 75% but notice a 50% type is cheaper.

    • Hi Adam, use the higher powered shock when you want more powerful shock? We have the standard 65% pool shock, and our Super Shock which is 73%, the highest level allowed by law. Super Shock costs more, but is in line with the higher potency, so it’s not really more expensive, looking at it that way.

  66. Alexa Marchinski

    So I’m not sure where my alge lies in these lines? If it’s algea at all.

    I have 40,000 gal in ground vinyl lining with cartrige filter.

    The water is blue but cloudy I can see the bottom.in the shallow at 3 ft but not the deep at 12 feet.

    pH: 6.8
    Fc: 0.3
    BRomine: 1
    Tc: 3
    Cc: 2.7
    All : 50

    What the heck am I doing wrong to get it clear ???

    • Hi Alexa, the chemistry readings you have posted are not good. When TC is higher than FC, higher than 0.3ppm, shocking the pool to 10x the level of combine chlorine (2.7) is required to rid the pool of the chloramines. To reach 30 ppm roughly, add about 16 lbs of cal hypo shock (yes!). Secondly, raise the alkalinity to 100 ppm, using Alkalinity Increaser, which hopefully will raise the pH level to 7.2-7.4. Also want to be sure that you have a good level of cyanuric acid, aka stabilizer, in the range of 30-40 ppm. Finally, unless you have a very large cartridge filter, of 350-450 sq. ft. – I would guess that your filter cartridge(s) may be needing replacement? Filter cartridges don’t last forever, and should be replaced every few years. Good luck!

  67. Matt Deutschlander

    Hello, opening a pool for the first time and I just cleaned and drained the pool and have now refilled. Do I need to shock it and add normal chlorine granules or just one or the other? 27,000 gallon vinyl oval

    • Hi Matt, when refilling with fresh water, if it takes a few days to fill, you may not need to do a complete shock, but you do want to get chlorine in the water fast, before invisible algae and bacteria have a chance to gain a foothold. Add 1 lb of granular pool shock, to raise chlorine quickly, tablets will take too long. Also with new water, the stabilizer level will be zero, so add 5-6 lbs of cyanuric acid to help protect the chlorine from the sun. And of course, also test and balance pH, alkalinity and calcium hardness levels with fresh water, which may be outside of recommended levels. Then start treating daily with chlorine tablets.

  68. Angelica Valdivia

    Hi i have a 3000 gallon pool it was turning light green so i bought a 13.3 oz bag
    Poured in a little more than half of the pack im worried i poured in too much? How lo g will it take untill i see results?

    • Hi there, results should be immediate, or a common bit of advice I give it to keep adding until you see the water turn a blue-white color. For clear water or light algae the general dose among chlorine shock treatments is 1 lb (16 oz) per 10,000 gallons. For medium algae double the dose and for sever algae triple dose or even more, if visiblity is very low and solids are high (debris in pool). A good low pH level of 7.2-7.4 is important, for the shock to be most potent. If your pool is still green, check the pH and chlorine levels, and then add the second half of the bag. Be sure to run the filter non-stop until things improve.

  69. Hey I have a 20,000 gallon vinyl pool it was a dark green I have been treated it for a week now I have done shock and liquid chlorine I’m at a light green now how long does it take change back blue and what I’m I doing wrong? My filter has been running for 96 hours now or more.

    • Hi Greg, needs more chlorine! 🙂 Keep adding until the water turns a blue-grey color. Lower the pH level first, if above 7.6, as chlorine is more active at lower pH levels, but keep it above 7.0. Keep running the filter, and hit it hard with chlorine, could take as much as 10 lbs of shock, depending on how strong the algae and other contaminants are – which so far have been able to sustain the chlorine levels added previously – show it who’s boss! 🙂

  70. I have a question regarding when you can safely go back into the pool after a partial shock Treatment. I have a 25,000 gallon in-ground pool. I added only I lb of granular shock to reduce some very light algae starting on the sides of the pool. I thought I could jump in after 2-3 hours but now I my skin is itchy.

    • Hi Bob, the itch could be from chloramines, or combined chlorine, and not free chlorine. Or it could be from undissolved chlorine particles. If you can test for Total Chlorine and Free CHlorine, if TC is higher than FC, that indicates the presence of chloramines, TC-FC=CC. If a noticeably difference is found, add 15x the amount – for example if CC = 1.0 ppm, add 15 ppm of chlorine (with shock), to reach breakpoint chlorination, where the CC molecules will be broken apart.

  71. Michael Stone

    Hi, have been reading your blogs and the comments . Our algae bloom is dark green. PH was 6.8 . 15,000 gallon. Inground pool.Yesterday shocked with 10 gal of liquid chlorine. Brushed, vacuumed & ran filter all night. No improvement this am. Added 2 lbs of shock & 7.5 gallons liquid chlorine, cleaning filter every 2 hours, no improvement, added 7.5 more gallons chlorine 3 hrs ago -no improvement. Just tested ph & it is now 7.8! Added 1 quart of Muriatic acid. Going to store to buy more shock and chlorine, what would you recommend we do at this point? Thank you, Sincerely, Michael Stone

    • Hi Michael, all that bleach raised the pH, as liquid chlorine has a high pH, around 13. I suspect that the source of liquid chlorine may be selling old stock – If you put in 25 (!) gallons of liquid shock, presumably 12.5% POOL bleach, aka commercial liquid chlorine, your levels should be very high, with no hint of algae, in a (small) 15K pool. Liquid chlorine has a low shelf life, loses potency within months, and after a year it could be much lower. However, perhaps your algae bloom is so bad, that even with full strength chlorine, it just laughs…? Can you pump out half the pool and refill? Can you drain the entire thing? Water is cheaper and faster than chemicals, I like to say – otherwise if not, I’d switch to dry granular pool shock, the 73% strength, like our Super Pool Shock, and hit it with about 5-7 lbs, and see what happens…

  72. Hi
    I have a 14ft round bestway pool which has turned green I put algaecide in but it did nothing how much shock should I put in ?? It’s also heated so would that make it go green all the time??

    • Hi Emma, algaecide, despite the suffix ‘cide’, meaning ‘to kill’, makes a poor algae killer. First step in any algae bloom is to lower the pH to 7.2, and then use granular or liquid chlorine to kill the algae. Keep adding until pool turns blue-ish, within 5 minutes. That’s usually (per 10000 gals of pool water) 1-2 lbs/gals for light algae, 2-3 lbs/gals for medium algae or 4-5 lbs/gals for heavy algae. Add more if there is leaf debris in the pool. Then run the filter non-stop, 24/7, adding a clarifier after 48 hours. Brushing and vacuuming of course, to remove the dead algae and shock dust. Vacuum ‘to waste’ if you have a multiport valve on a sand filter

  73. I have a 16×48 vinyl pool. Our water is medium green. I’ve read alot of comments. What do you do to either rise or lower your ph to get ready for chlorine? Also do I shock and do chlorine tablets to get it cleaned out?

    • Hi, chlorine works best at a lower pH, adjust to 7.2 for maximum effect when treating for algae. When shocking the pool with granular chlorine, you don’t need to use tablets at the same time (separately, in a floater or chlorinator), but after 24-48 hours the chlorine level will drop again, and assuming all algae has been killed, you can switch to tablets, used constantly to maintain a consistent daily chlorine level of minimum 1.0 ppm. IF the algae has NOT all been killed by your first shocking, you may have missed the mark – keep the tablets in the bucket and shock again, with 1/3 to 1/2 more this time…

  74. Hi! We’re opening our pool after a long winter. We have a sand filter. When we took off the cover the water was dark green. We took a sample of water to the pool store. They said our levels weren’t bad except for 0 chlorine. We went through the steps they advised but our water is a lighter green and hasn’t cleared since. I see in previous comments I should continue to shock the pool. My questions is how often should I add shock to get the water blue?

    • Hi Vanessa, it’s not really how often, but how much – that is the question. Depending on the severity of the algae, (color, visiblity, level of debris in the pool), a shock treatment can vary from 2 lbs to 6 lbs, per 10000 gallons of water. Very important is to have a good pH level (LOW pH level, 7.2-ish), so that chlorine is most potent. Keep adding the shock until (within 10 minutes) it turns a blue-grey color. Also important to filter the water nearly non-stop, cleaning filter only when flow rates are reduced, and possibly replacing filter sand afterwards. Sand Filters, especially small tanks under 24″ dia. aren’t very strong performers, so using a clarifier, or the Slime Bag, are good products to improve filtration.

  75. Stephanie

    Our pool will not hold an acceptable chlorine level. We have cleaned it and shocked it several times now. What could be the problem? Ph and other levels fine.

    • Hi Stephanie, even though you said all levels are fine, let me ask about stabilizer or cyanuric acid for the benefit of the readers, if too low the sun can burn off chlorine quickly, and if too high (over 100 ppm usually) a chlorine reading can become difficult to obtain. Best range is 30-40 ppm of stabilizer, aka cyanuric acid. Second thought is that test reagents or test strips do expire and could be giving you false readings. When those ideas don’t pan out, it can be high levels of phosphates/nitrates in the water, over 300 ppb and a phosphate remover should be used, ‘consuming’ the chlorine, or high levels of nitrogen/ammonia converting chlorine into chloramines – if you can check Total Chlorine vs. Free Chlorine, the difference between the two is Combined Chlorine, or chloramines. Often in cases such as yours, the solution is to triple shock the pool, using 3-5 lbs of granular chlorine for every 10,000 gallons, or an equivalent amount of liquid pool shock, to reach a breakpoint threshold where everything is oxidized or destroyed.

  76. Maxine Rossi

    I have a in ground pool filled with well water. What would you suggest to kill dark green algae? I have been working on the pool for a year now. I have been removing the leaves and mud off the bottom of the pool, making progress. I inherit the pool and it hasn’t had care for at least 10 years or more.

    • Davy Merino

      Hi Maxine, draining and refilling the pool with fresh water, after a thorough cleaning and acid washing (cement pools only) is my best recommendation. If draining is not possible, then a very heavy dose of chlorine, with a pH level in the 6.8-7.2 range is the next best step, after removing all of the organics (solids, leaves and mud). However, there will be stains, lots of stains, and the water – is so choked with solids, that fresh water is really the best long term solution, to avoid continued algae and water quality problems. Also, be sure the pump and filter is operating properly and ready to go for the fresh water. The filter media (sand or cartridges) likely need to be replaced also… good luck – let me know if there are additional questions!

  77. Sherri Brickey

    I added 4 gallons of bleach and 2 bags of shock to a 15000 gallon pool to kill algae. How long before I can swim.

    • Davy Merino

      Hi Sherri, the main concern with shock is that undissolved granules may get into your eyes or ears, or irritate skin, esp if it gets stuck in between your suit – ouch! High levels of chlorine can also fade swimsuits and lighten hair. Your test kit could tell you – when it drops below 5 ppm, and granules are dissolved, it’s ok to swim. At 10 ppm, you may fade out your favorite swim suit, or experience skin irritation. In most cases, this is 24 hours, but you added quite a bit of chlorine, may take 48-72 hrs to drop…

  78. Hi I have a 20k gallon pool. Slight algae showing up on sides. Tested the water and ph is 7.2, free chlorine is at 0, alkalinity is at 70, phosphates are at 750 ppm. How much chlorine should i add. I would prefer liquid chlorine and have 2 gallons of 10%. Water is clear still. I just want to get my chlorine back to 2.0-3.0, my ph back up to 7.4 and my phosphates back below 100ppm. Thanks for the assistance.

    • Davy Merino

      I would first lower the phosphates, with a phosphate remover chemical, well actually, you better get some chlorine in there fast. 1/2 gallon should raise the chlorine to above 2.0 ppm, but the phosphates will consume some – then treat with phosfree or other remover, and then add more chlorine. Liquid chlorine produces the same hypochlorous acid as tablets, but it is hard to treat consistently – unless you are using a liquid chlorine feeder ($$$). If you want to stick with liquid (instead of tablets), it probably should be added at least once daily, to avoid peaks and valleys in chlorination. Also – try to find the source of phosphates if possible (fertilizer, mulch, soil…)

      • I have been using tablets in a floater and been able to maintain my chlorine level at 2.0 ppm all summer till now. We did go out of town and came home to an empty floater though. Im guessing the phosphates are coming from the leaves from our 2 shade trees and the dust that gets blown around regularly here in Arizona during monsoon season. I added slightly over half a gallon and will test it later today. Should i clean cartridge filters before and after adding phosfree or just after?

        • Davy Merino

          Josh, I’d suggest cleaning them first, if the pressure is 5+ psi higher than normal, if normal wait until 48 hours after treatment, unless the product label advises differently.

  79. Hi
    I just have a kids pool….intex 15ft x 33 inches round.
    I use the chlorine tablets….but now water is turning green.
    How much shock do I use?
    I bought a 1 lb bag.
    I think it is 2600 gallons of water

    Thanks for any helpappreciate it
    DIANE 😊 .

    • Davy Merino

      Hi Diane, use 1/2 lb, and then seal up the bag tightly inside of a ziploc, to keep out moisture and prevent spills. Before adding, check and adjust pH if needed, to be in the low end of the range, around 7.2-7.3. Predissolve the shock into a 5 gal. bucket of water, then pour around the pool, then brush pool, and run filter for at least 4 hours, if not overnight.

  80. Jackie Sullivan

    I opened my pool about a week ago. It’s still green. I’m running my DE filter 12 hrs a day. I have a 27,000 gallon pool.. Help!! How much shock should I add. Should I dilute it or juse sprinkle it in

    • Davy Merino

      Hi, if it’s still green, you need more shock – keep adding until the water turns a blue/gray color, then add one more. For your pool, that should be 10 or 11 lbs of shock, to reach 30 ppm. You can pour it right into the pool if you have a concrete pool, vinyl pools should predissolve. Make sure your pH level is low, around 7.2, for best results or potency from the shock. Run the filter 22 hours per day, until clear.

  81. is super pool shock safe for vinyl liners as is or do you have to dilude it first

    • Davy Merino

      Super shock is a Cal Hypo product so it should always be diluted by pouring into a full 5-gal bucket of water, stirring to dissolve and then pouring around the edge. If any granules fall in the pool, use a pool brush to push them around. It is the strongest shock we sell also, so be careful not to overdose the pool. I think I would recommend just regular pool shock, and not super pool shock, 65%, not 73% – for a vinyl pool, just to protect the colors of the vinyl.

  82. Hi, this if the first time we are opening a pool. I tried to get my husband to hire someone, but he insists on doing it himself. YouTube told him he could. Our pool is “dark green”, 25000 and the deepest end is 8 ft. The deep end is so dark it looks “hunter green”. We’ve been running the pump for 2 days now and he added the chlorine and two bags of shock (which is what the bag said we needed for our size pool). We also ran the pool vacuum all day yesterday. There has been no change. Three questions, how long after adding the shock should we see a change, should we have used more than two bags of shock and it said to clean the pool first, but the bottom is so dirty we can’t tell if there is anything down there other than algae, if there is, will it undo what we have done with the shock?

    • Hi Gwen, the two bags of shock didn’t do much, and were wasted unfortunately. The pool just ‘ate it up’. Here’s what to do. First make sure that the pH and alkalinity levels are good, best range is 7.2-7.4 for pH and 80-100 for alkalinity. Then, shock the *&^% out of the pool, with about 6 to 10 lbs of pool shock. Just keep adding until the water turns blue/grey color. Run the filter all night. In the morning, clean the filter and recheck pH and chlorine levels. If chlorine is at zero, but pool is still blue-ish and cloudy, add 2-3 lbs of shock. If it is zero but has turned green again, add another 5-6 lbs of shock. (I know it’s a lot, but trust me you need it!). Keep pH balanced, run filter for 24/7, add a clarifier a few days after the final shock. You’ll get there! I applaud your DIY spirit!

  83. Harry Wise

    My pool store told me to add 40 pounds of your shock to my 25000 gal pool for a no chlorine condition. Have you ever heard of having to add such a huge amount?

    • Hi, not for a no-chlorine condition. If your pool has very bad algae, I mean very bad – it may take 40 lbs, but if the water is clear, you can add just 1 lb, to raise the chlorine level again. A normal shock treatment is generally 1 lb per 10000 gallons of pool water, or about 3 lbs for your pool. For visible algae, 5-6 lbs may be called for, and for very bad algae or ‘tea’ colored water, up to 10-12 lbs is not unusual – but 40 lbs? They might be confused…

    • Brian Howard

      Ask them to check your stabilizer as well. That can cause the chlorine to not release. Just a thought good luck!

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