How to Reduce Pool or Spa Chlorine Levels

how to reduce pool or spa chlorine levels

Maintaining the correct chlorine level can be tricky. And when super-chlorinating or shocking the pool to remove algae, bacteria, and chloramines from the water, it’s very easy to overshoot the mark and over-chlorinate the pool.

Ideal pool chlorine levels are generally in the range of 2.0-4.0 parts per million (ppm). If your pool water is much higher than 4.0-5.0 ppm, keep reading to learn what you can do about it.

Why is My Chlorine Level So High?

high chlorine levels

Adding too much pool shock or putting too many chlorine tablets to the feeder can both result in very high levels of chlorine. Another common way to over-chlorinate a pool is to leave a liquid chlorine pump running all night – you’ll often come in the next day to discover a greenish-looking pool.

Correct levels of chlorine stabilizer (Cyanuric Acid or CYA) will protect chlorine from the sun, and will slow the natural degradation of chlorine. CYA should stay in the ideal range of 30-50 ppm. If you find yourself having to add more stabilizer to the pool, slightly reduce the amount of chlorine used after application. Otherwise, you may find yourself accidentally adding way too much chlorine to the pool. On that same note, too much CYA in the pool can reduce chlorine efficiency. You may even get an inaccurate chlorine reading. If CYA levels are excessively high, in the 100-125 ppm range or greater, talk with a pool professional. You may need to consider diluting the water to bring levels back down.

Different times of year require different amounts of chlorine or bromine. On hot and sunny days, your pool will use up chlorine more quickly. The same holds true for pools with more swimmers and heavier leaf debris – you’ll need more chlorine to maintain a consistent level of sanitation. On the other hand, swimming pools with efficient filtration and circulation systems, or pools with secondary sanitizers like minerals, ozonators, or UV systems, may require 50% less chlorine to maintain clean and clear water.

How High is Too High for Chlorine?

pool care questions

Every person’s sensitivity to chlorine is different. When free chlorine is over 5.0 ppm, swimmers may experience itchy skin, irritated eyes, and/or dry hair.

Pools will naturally gas-off chlorine from the surface, and very high levels can irritate airways and lungs. This is especially true for indoor pools.

At chlorine levels over 10 ppm, swimsuits can begin to fade. Pool covers become damaged, and the water is generally uncomfortable and unsafe for swimmers. Close the pool and keep covers off until chlorine levels fall back below 5.0 ppm.

Testing Very High Chlorine Levels

check chlorine levels in pool water

When testing very high levels of chlorine, 10 ppm is the maximum detected by kits or strips. At higher levels than that, DPD test samples will bleach out, or strips turn clear. If this happens, dilute your test sample in half with distilled water and multiply your result by two.

For example, shake out half of the water test vial and refill with distilled water. Next multiply your test result x 2 to test for readings above 10 ppm. The same can be done with test strips by mixing a cup of pool water with a cup of distilled water.

How To Reduce Chlorine Levels in the Pool

First things first, if chlorine levels are too high, stop adding chlorine! Turn off your automatic chlorinator or remove your chlorine floater from the pool. There are a few different ways to lower the chlorine levels in your pool:

  1. Remove chlorine naturally with sunlight, aeration, and agitation of the water.
  2. Add Sodium Thiosulfate, a.k.a. Chlorine Neutralizer, for instant reduction.
  3. Add Ascorbic Acid, a.k.a. Vitamin C, to remove chlorine.
  4. Add Hydrogen Peroxide to break down chlorine.

The least expensive option is to allow the chlorine to dissipate naturally. After shocking the pool, leave the water uncovered, and allow the chlorine time to gas off on its own. Aerating the pool and circulating or agitating the water will help excess chlorine dissipate more quickly. But if you’ve accidentally added too much chlorine shock, and you need to use the pool sooner than later, there are a few other methods will help get you back in the pool faster. Pools located in shady areas may not be able to use this method reliably since it’s largely dependent on direct sunlight.

In The Swim pool chemicals for reducing chlorine levels

When using Sodium Thiosulfate, add 2 oz. per 10,000 gallons of pool water to lower chlorine levels by 1.0 ppm. If using chemical methods to reduce chlorine levels, this one is probably the cheapest and most reliable method.

Ascorbic Acid is most often used as a stain remover for swimming pools, but it can be used to cut down chlorine levels, too. A 10 oz. dose per 10,000 gallons of pool water will lower chlorine levels by about 3.0 ppm.

Hydrogen Peroxide helps to break down chlorine, but works best in pH levels of 7.0 or higher. Use 7 oz. of Aqua Silk Oxidizer (27% hydrogen peroxide formula) per 10,000 gallons of pool water to lower chlorine level by 3.0 ppm. For spas and smaller bodies of water, use 1 oz. of 3% drug store grade hydrogen peroxide per 100 gallons of spa water to lower chlorine (or bromine) levels by about 5 ppm. Remember that pH levels will drop after an effective hydrogen peroxide treatment. Be sure to rebalance your water when done.

When using chemical methods to lower chlorine levels in pools and spas, be careful not to overshoot the mark. Overdosing the pool with Sodium Thiosulfate may make it difficult to add new chlorine, at least temporarily. Sodium Thiosulfate will dissipate from most pools within a few days. Always refer to the product label for recommended water balance and correct dosage instructions.

Reducing High Chlorine (or Bromine) in Hot Tubs

The methods for reducing sanitizer levels in spas and hot tubs are much the same as the ones listed above. In many cases, just leaving a hot tub uncovered and running the jet pump on high with the air blower running can bring high levels down in just a few hours.

reduce chlorine levels in pool or spa

If this doesn’t work quickly enough, invest in a small bottle of Chlorine Neutralizer, which is also a very effective bromine reducer or neutralizer.

Remember that spas and hot tubs that use bromine can use higher levels of bromine with less side effects than chlorine. Bromine is 2.5x heavier than chlorine, meaning that a reading of 2.5 ppm bromine is the same as 1.0 ppm of chlorine. Most hot tubs using bromine should maintain a 3.0-5.0 ppm residual, or 1.0-3.0 ppm if using mineral sanitizers or ozone.

How high is too high for hot tub bromine? Sensitivity differs by person, but most folks can manage short duration soaks in hot tubs with bromine levels of up to 10 ppm (or chlorine levels of 5 ppm), without significant skin irritation. However, high bromine levels also leave a strong odor on skin and hair. This alone may be enough to prompt you to lower the levels.

Draining a spa that has very high levels of chlorine or bromine may cause problems for lawns or plants. Pumping it into a swimming pool (chlorine only), or directly to a storm drain are two other options. You can also dilute the water by partially draining and refilling the spa or hot tub.


To keep this issue from happening again, it often requires a change in your pool or spa management protocol. Extended periods of high chlorine or bromine levels can be detrimental to the health of your pool, equipment, and accessories like covers and floats. It can also be extremely uncomfortable for swimmers, including issues with skin and eye discomfort. Keep your water properly balanced, read and follow chemical label instructions, and understand the correct dosage measurements based on the size of your pool or spa.

49 thoughts on “How to Reduce Pool or Spa Chlorine Levels

  1. We recently purchased the coleman inflatable hot tub. We filled the hot tub and got it up to temperature, then we added our chlorine floater with one 3in chlorine tablet. We tested the water the next day and the chlorine level was high, >5. We removed the floater and allowed the level to go back down (chlorine was pretty much gone in a day). Put the floater back in and it goes right back to being way too high in less than a day. Why is the chlorine increasing at such a rapid rate and not stabilizing?

    • The size of the tablet is too much for a small tub. You can break the tablet into smaller chunks, or you can leave the tablet inside of the plastic wrapper, and cut open one or two corners of the bag with scissors, then put it in the floater. Next time you buy, look for the 1″ tablets.

  2. Hello Davy, I believe I have high chloramines levels in my pool. It will not hold chlorine and is eating up stabilizer. How much Sodium Thiosulfate should I use to lower it? pool is 10k gallons

    • Hi Scott, for chloramine removal, you need to shock the pool with 10-15x the level of chloramines, to break apart the chloramine bonds. Since you cannot hold chlorine, I would suggest a ‘triple shock’, or 3 lbs of granular chlorine, with a suitably low pH level of 7.2-ish. Check chlorine level the next morning, if it is near zero, repeat with 4 lbs of chlorine.

  3. Hi
    Today I put a test strip into my pool and all level are in the range except for free chlorine which is at around 10.
    My pool is chlorine and it also has a chlorinator. The chlorinator was flashing low salt.
    Will adding a bag e.g 20kg into the pool fix the ppm to the correct level?
    Many thanks!

    • Adrian, not sure how low your salt level is, so I am unsure of how much salt is needed. If your salt system does not display a salt level in ppm, you can obtain salt test strips, to determine current salinity level. 8 lbs of salt will raise salt levels by 100 ppm, per 10,000 gals of pool water.

  4. Hello
    I shock my pool,but I forgot to turn on the pump now my pool is cloudy and my chlorine is very high please what can I do thanks
    my pool is plastic and has 2500 gallons because it is 15 * 36 thank you

    • Hi Nelida, no worries the chlorine level will go down over the next few days. For the cloudy, keep running the filter 24/7, and using some Clarifier can help, per label instructions.

    • Hilary Schwartzler

      Hello, we recently purchased a home with a pool and want to self maintain. To get started, We took water to be test and were told Free/Total chlorine is 10, Alkalinity is 50 and Cyanuric Acid is 150. They said our only option is to drain the pool, is there a simpler way to fix this possibly naturally? I appreciate any help you can offer!

      • Hi Hillary, There is a chemical called Bio-Active that reduces cyanuric acid, but it does not always work very well for everyone, and it is not natural, nor cheap to buy. Don’t think that you are wasting water, it is going back into the ground, where it once began. Draining would be the easiest solution, and make the pool much easier to manage. Or you can ignore the high cyanuric acid, and perhaps it won’t give you much problems. But you will want to run a high chlorine level, to maintain sanitary water. 5-7 ppm would be about right. And also would want to raise the alkalinity level by adding some alk increaser, to reach about 80 ppm. Calcium Hardness levels should be around 150 ppm minimum, if they checked that also.

  5. Amanda Hamm

    Hi there!
    I am having a chlorine issue! My total chlorine is 10 ppm and my free chlorine is 5 ppm. I’m not sure what to do!! Should I shock my pool?

    • Yes, when total cl is 0.3 ppm more than free cl – it’s time to shock the pool. Shock it to a level that is 10x the level of combined chlorine, which in your case would be a very high level of 50 ppm. Test again, to be sure CC is 5.0 ppm, then lower pH to 7.2 and shock the pool with 1.5 lbs of Cal Hypo shock per 10,000 gallons, for each 10 ppm of free chlorine you require. For 50 ppm, for example, that would be 7.5 lbs of shock (!) per 10,000 gals of pool water.

      • Amanda Hamm

        Hi again!
        That seems like a lot of shock! Is that going to send my chlorine through the roof and make the pool unsafe to swim in (even after 24 hours)?

        Your help is appreciated 😊

  6. Shannon Panagos

    Hi! I am in need of help. I have a Zodiac approximately 14,000 gallons inground pool. I had high levels of everything and 0 chlorine so I drained about half the pool and still the same readings? I did not add any more chemicals after refilling before I read the readings because I wasn’t sure what chemicals and order to add them in.
    Can you help me?

    • SHannon, you can test your tap water, to determine if the levels are different than the pool. I would add chlorine right away, to prevent an algae bloom.

  7. Hi there! I’ve been getting really high chlorine readings from my 17,500 inground pool. I have not shocked it in 2 weeks and have not had a chlorine tab in for a week and still the chlorine levels are off the charts. I have the automatic feeder running, without any tabs in it. No seems to be able to help me solve this problem!

    • Tara, that is an unusual question. If you had recently added cyanuric acid and a large shock treatment, it could last for awhile. two weeks? Maybe someone else has been adding chlorine? Or tabs in the skimmer perhaps? I would expect the level to fall very soon…?

  8. Helga Kulkarni

    Hello!
    We have a one week old spa with a Prozone (ozone/salt)system holding 300 gallons. We had our water tested at a local pool and supply store. They said our chlorine was extremely high (Free 12.5 and Total 14.2, but the . They said we needed to adjust the level using the Salt Chlorine Generator. Our spa does not come with that feature. What do you suggest we do? Also, we are getting a ring of dirt clinging to the sides of the acrylic where the foam at the top of the water level touches it. My husband and I don’t wear lotion or oils, etc., so are unsure of why or where this dirt ring is coming from. Any suggestions would be much appreciated.

    • Helga, sounds like it is time to drain the spa – when it begins to foam and produce waterline scum, is a good indicator.

  9. Jamie Barker

    I have a small pool 8, round 2’ deep. I filled the floating chlorination w tablets and let it float for 2 days. Now the chlorine and free chlorine are way too high. How do I bring it down? No one gives calculations for such a small pool. I’m at the store and they have chlorine stabilizer, pH up, pH down, alkalinity increased, calcium hardness increaser, and baking soda. What should I use?

    • Hi Jamie, the chlorine will come down on its own in another day or two. Run the filter, that will help. The article gives several other options to reduce chlorine levels. Thankyou for the comment!!! Good luck with your small pool.

  10. Crystal Joseph

    I have a 14 ft swim spa that holds about 1600 gallons of water. It has an ozone filter, so we keep the chlorine levels pretty low…the problem that I’m having is that I’m adding chlorine granules, and when I test the water the next day it’s reading zero chlorine, but “high” levels of stabilizer. (But I didn’t use any stabilizer) wondering why my chlorine is being read as stabilizer by the test strips…?

    • Hi Crystal, are you using Di-Chlor granules? That is stabilized shock that contains cyanuric acid. If the stabilizer is high it may be creating a chlorine lock. In such case, I would drain most of the water and refill the swim spa. If that’s not the case, it could be a build up of ammonia or nitrates that are consuming the chlorine, and a triple shock would be the best step, (3x shock dosage) to destroy these contaminants.

  11. Michael D

    Davy,

    We have a 18′ above ground, round pool. Approximately 7600 gallons. Total chlorine is at 5 and free is at 3. If I am understanding all I have read, my combined is 2. Is this correct? Is there anything to do. Chlorine smell is present but pool has been under cover for three days. We had to shock and add algaecide to kill bloom after rain storm. Water is clear and all other levels seem to be in range other than stabilizer being low. Any direction is greatly appreciated.

    • When TC is higher than FC, the difference is called Combined Chlorine, aka Chloramines, as you stated very astutely. When CC is 0.3 ppm or higher, it is thought to be too high, and shocking the pool is recommended. When you have 2.0 ppm of CC, it is really recommended! 🙂 Combined Chlorine (CC) do not actively sanitize, all they do is take up space, smell up the space and irritate eyes (and lungs). To remove CC, shock the pool to a level 10x the amount (at least). In your case, you want to shock to 20 ppm, to get rid of 2 ppm of CC. For a 7600 gal pool, use 24 oz of Cal Hypo 65% pool shock, or about 1.5 lbs, (or 2 bags) predissolved in a bucket of water then pour into the pool. Then brush the pool and run the filter. Check pH first before shocking, as chlorine is much more potent at a low pH of 7.2-ish.

  12. Kara wells

    Hi Ron, I have a very above ground kids pool only about 800 gallons that I shocked with too much chlorine. Would 3% hydrogen peroxide work to bring the level down to 4ppm? I’m not sure what the current ppm is but the test strips show it’s in the highest category and dark purple. Help!

    • Hi Kara, hydrogen peroxide is one way to remove chlorine, but the 3% drug store variety is not very strong and may do nothing. I would suggest draining and refilling most of the water. If you can drain to a rocky area, or to a storm drain, the high chlorine won’t be a problem. Then refill with fresh water.

  13. Thomas Reaves

    I have a three-week old 9,000 to 10,000 gallon salt water pool. My free chlorine reading is 7.5 ppm. I added stabilizer today and my understanding is that I need to run the pool pump for 24 hours after adding the stabilizer. I don’t want to increase the chlorine level. Should I turn off the chlorinator or reduce it to a lower level (been running it at about 30-40%)?

    • Thomas, yes shut it off altogether, you will notice that the cyanuric will make your chlorine last much longer, and you may not need to add any for a week. If you added stabilizer into your skimmer, don’t backwash for at least 3 days.

  14. Hello Davy..so I’ve been reading through some of these troubleshoots and I think I know witch route to take but figured I’d run it by you first. So my chlorine appears to be extremely high showing a dark orange color in the test. My pool is not real fancy or big it’s only a 14 foot 3300 gallon above ground and I just bought and put it up a few weeks back..I have not added any chlorine other then my tablet floater. So that being said should I get a chlorine neutralizer or just let it run it’s course. One other thing is there really isn’t a strong Oder of chlorine and my PH seems to be reading in the normal range. One other thing I have 3 different strip type tests and every single one gives me different results one shows ideal chlorine one shows high chlorine and my drop test shows extremely high. I’m at a loss here any help will be greatly appreciated thank you in advance

    • Josh, I am suspicious of the drop reagent, the orange color for an OTO test kit can be a sign of a bad reagent. Especially if you have not shocked, just used tablets. I suspect you are not far off the mark.

  15. Hi Davy. I started the pool by adding pool shock 2 cups for a 10,000 pound of water. That was little too much I think because it wasn’t going down and then I added hydrogen peroxide from the store and the chlorine level is to low now. Can I add more pool shock .

    • Yes, you can add more pool shock, but don’t use peroxide in the pool, that is for other treatment methods that use biguanides, not chlorine. Remember the 2016 Rio Olympics Green pool fiasco? They say it was caused by adding peroxide, by mistake. Anyway, no need for that stuff in a chlorine pool. You are using tablets right? You need a daily chlorine product, and shock is too quick acting, creates highs and lows, and tablet give a consistent chlorination level.

  16. Don Holmberg

    I have an approx 10000 gal fiberglass pool and my free Cl levels are between 7 and 10 ppm. Total Cl wasn’t measured but it is high also. My need is to get the Cl (both) down to about 1ppm in order to add cobalt and iron treatment and metal control.
    Our local water dept uses Chloramine to sanitize our water so adding water isnt necessarily going lower the total chlorine is it? I would have to practically drain the pool! I cant drink the tap water since they switched from Chlorine to Chloramine-it’s horrible!

    • Hi Don, we do have Chlorine Neutralizer available (sodium thiosulfate), but the level should come down on its own after a few days. Stop adding chlorine, if you haven’t already. A few sunny days will deplete the Cl level.

      • Don Holmberg

        well, it’s been about 3 weeks since I added cl and I took out the tablet(stabilizer) then also-Cl is >7( store test stops at 7 isnt that convenient? So I have had an issue w/ high cl before but 3 weeks to a month in sunny fl and no drop in Cl? Hmmm… frustrated

        • Don, are you sure your test kit or strip is correct? Or the store may be wrong? You should get some strips to cross-check yourself. Does the water smell of chlorine? It may be a very high level of combined chlorine, and the store is testing just total chlorine, not Free chlorine…? 3 weeks is a very long time for chlorine to persist in sunny outdoor.

  17. Richard Baxter

    Does chlorine neutralizer reduce just combined chlorine or does it reduce free chlorine as well? I called Intheswim and I was told it just reduces the combined chlorine but your comments make it sounds like both. I wish the info about it on your website was clearer. The woman I spoke to didn’t really sound too confident about what she was telling me.

  18. Hi, my baby pooped in a pool by accident last Friday. I went to pool supply store and they recommended me to have pool shock. My pool is about 12000 gallons and they gave me 2 packs of 73% chlorine shock plus products. I pour 2 packs into my pool and kept running filter pump 7-10 hours a day last few days. After 7 days, chlorine level for my pool is still 10 ppm. (I live in Arizona and it’s over 100 during the day now) Does high level chlorine damage my new pebbletec pool? I still have no idea why the store recommended that much chlorine.

    • Hi Jenny, that’s ok, and a good recommendation for a ‘fecal event’. Give it a few more days, the chlorine should come down on its own. It is odd that it stays that high for so long, perhaps your reagents or test strips are faulty. It won’t damage the pool. It’s good to be sure that the poop has been neutralized.

  19. Hi Davey; does this article apply to reducing ‘free chlorine’ only or does it apply to total and combined chlorine as well; I have high ‘total’ chlorine readings but normal ‘free’ chlorine readings from what I can see and trying to reduce total/combined chlorine levels in my hot tub.

    • HI deejay, great question, thank you! This article deals with removing ALL chlorine from the pool. If you are trying to remove combined chlorine (aka chloramines), so that your Total chlorine and Free chlorine levels are the same, that is done by shocking the pool to a level high enough to break apart the chlorine bonds. Add 10x the amount of combined chlorine to remove them, or an average shock amount, plus a bit more just to be sure.

  20. Doron Weisbarth

    Davy, that suggestion to use hydrogen peroxide with spot-on! It did the trick quickly and easily, with no side effects. I wish I had known this trick earlier, it would have saved me a lot of time and money. I have a 2900 gallon swim spa and we just replace the water. I made the mistake of adding some chlorine while it was filling up and it turns out I put in way too much. I had to dump out more than half of it and it was still high. The hydrogen peroxide just brought it down almost instantly. And all I had to use was one 32 oz bottle. I’m writing this because I want others to know this great trick. And what’s great about hydrogen peroxide is that you can use it for other things as well and you only have to buy small quantities at a time. Thanks again!

    • did you use regular hydrogen peroxide or a special kind for pools?

      • Peroxide comes in many strengths, the regular brown bottle stuff is only 3% usually. The stuff we sell as part of our Aqua Silk sanitizer system is much stronger or more concentrated.

  21. Ron Richardson

    Hi Davy. Thank you kindly for such an informative website! One question I had was in regards to what happens when I add shock. My spa water is clear, the Ph & alkalinity are fine, etc. I’ve built a bromide bank with a powder starter kit, and supplement with bromine tablets. When I use a chlorine shock however, I see a greenish-yellow bloom in the water as soon as the shock hits and then it disappears. I’ve tested for all metals (strips and at the pool store) and all is clear. Any ideas what this reaction is?

    • Hi Ron, I would guess that is the conversion of hypochlorous acid to hypobromous acid, and what a special thing it is! 🙂 I don’t think it’s a troublesome reaction, just part of the general chemical reaction between chlorine and bromides, converting into bromine. How’s that sound? 🙂

Comments are closed.