What Pool Chlorine Type is Best for your Pool?

How to buy the right type of pool chlorineFirst, let me put two misconceptions to rest. Chlorine for above ground pools is the same as chlorine for in ground pools and there is no one best chlorine for a particular pool type.

There are two simple questions that can help you determine what type of chlorine is best for you. Some of the choice comes down to preference. Starting out though, let’s get to the basics of what chlorine types are available.

Pool chlorine can be either stabilized or unstabilized. When many pool owners hear that their chlorine is unstabilized it conjures up images of beakers exploding in laboratories. With chlorine however, this refers to the addition of a chemical called cyanuric acid to the chlorine. CYA shields the Cl2 molecule from the sun, sort of like sunscreen for your chlorine.

So the first question should be, “Is your pool indoors or outdoors?” Indoor pools don’t really need stabilized chlorine, and neither do portable spas. For this reason, and the greater stability at fluctuating pH levels, these types may find benefit in using bromine, a close cousin to chlorine.

Liquid Pool Chlorine or pool bleach, sodium hypochlorite pool chlorine types, pool chlorine tablets or trichlor tabs pool chlorine shock, dichlor or cal hypo granular pool chlorine

Types of Stabilized Pool Chlorine

1” tablets, 3” tablets and slow dissolving sticks are the EXACT same chemical compound (Trichloro-S-Triazinetrione). So whether you call it a tablet, a puck or a stick you are getting the exact same product. If you have an outdoor pool you need the stabilized chlorine and per pound, the three inch chlorine tablets are the cheapest. Additionally, if you are using a chlorine feeder most are designed for the three inch chlorine tablets. So to get the most chlorine in your feeder at one time use the three inch tablets.

Why would you use the 1 inch tablets or chlorine sticks? This comes down to surface area; when you place the one inch tablets or sticks in your feeder they don’t line up as smoothly as the three inch tablets do. What this does is gives more surface area for water to erode the tablets – thus increasing the chlorine level more quickly. Another use for 1″ tablets is for chlorinating spas or very small pools, in which case a 3 inch chlorine tablet may be too large.

The other form of stabilized chlorine is a certain type of pool shock. While granular still has the stabilizer in the chemical compound (SodiumDichloro-S-Triazinetrione) the difference comes in the percentage of available chlorine and the effect of granular chlorine on the pool water. Stabilized chlorine shock or granular should have 56% available chlorine. What it lacks in potency it makes up with by having virtually no effect on your pool water pH level.

Types of Non-Stabilized Pool Chlorine

Liquid chlorine (sodium hypochlorite) – popular in many parts of the country, has some complications in its use.

  1. It is only 10-15% available chlorine, and has more sodium than chlorine.
  2. It is the fastest acting due to the fact that it is pre-dissolved.
  3. It is un-stabilized or unprotected against the sun’s UV rays.
  4. It requires a specialized feeder or the pool owner to pour it into the pool.
  5. Pouring it directly into the pool will cause the chlorine to have peaks and valleys instead of having a steady safe level.
  6. Increases pH Levels dramatically, with a pH level of 13.

Pool shock can also come in other granular forms that are not stabilized, such as calcium hypochlorite. Cal Hypo, as it’s called, has a higher level of available chlorine, at 65% – but is not stabilized, or protected from the sun. A real Grade-A Fancy pool shock, lithium hypochlorite – is only 35% available but is fast dissolving, suitable for pools with vinyl liners, but also non-stabilized. Non chlorine shock, usually potassium monopersulfate, is also unstabilized because it’s, well…non-chlorine.

All pool shock granular products should be used for superchlorination and not as an every day chlorinating method. The burn rate is very fast, and like eating Chinese food – your pool is soon hungry for more.

One thing that all chlorine types have in common is that when they dissolve in water, they produce hypochlorous acid which is the active ingredient in chlorine. Without it, contaminants, organic matter, viruses and pathogens begin to grow in any untreated body of water.

I’d be remiss if I failed to pass along a bit of safety information about pool chlorine:

  1. Never mix different chlorine types together. They will react violently.
  2. Follow all label instructions when transporting, storing and using chlorine.
  3. Never allow dirt or any foreign substance or debris to contact chlorine.
  4. Keep chlorine in a cool, dry location, away from children.
  5. Never allow any other pool chemical to come in contact with chlorine.

So, in answer to the question: “What type of chlorine is right for me?”, consider your pool size and location. Outside of that I like to tell people, Buy the best chlorine at the lowest price, look for a low cost stick or tablet, from a company you like, and you’ll be fine.

Enjoy your Pool!




Brett Rotelli
IntheSwim Staff Blogger


What Pool Chlorine Type is Best for your Pool? — 17 Comments

  1. Hello, I am wanting to change the type of chlorine in my pool from a stabilized chlorine to an unstablized chlorine. What is the safest way to do this?

    • Hi Mickey, good question. The first thing that comes to mind is to install a saltwater chlorine generator and ‘go saltwater’. Secondly, you can install a Cal Hypo tablet feeder, like the CCH Feeder, which uses a specific Cal Hypo tablet, without any cyanuric acid. A third way would be to purchase bleach from a local Sodium Hypochlorite supplier in 5-gal containers, and use a chemical pump, like the Blue-White or RolaChem, to pump from the container, directly into the pool line, a 12.5% bleach solution (without cyanuric acid). A fourth way to do it would be to reduce the need for chlorine, by installing a large DE filter, Nature2 Express, and/or an Ozonator – then just shock the pool weekly, with chlorine or non-chlorine shock, (or use 1/3 as many tablets, which reduces the buildup of cyanuric). With exception to the last method, you will need to add a few pounds of cyanuric every so often to keep levels at 20-30 ppm, but it won’t add any to the water.

  2. Dear sir.hi I have an issue with my pool.CYA amount in my pool is 120 ppm.to Lower the ppm below 100 I am to only use shock and stay away from chlorine tabes.my pool is 12000gal.outdoor, and I live in Arizona, Hot.Hot

    Thank you Henry

    • Hi Henry, to reduce cyanuric acid levels, the solution is dilution, drain and refill a portion of the pool to lower cya levels. You can also use Bio-Active, an new product that claims to reduce cya by up to 50 ppm, for a $50 cost.

  3. We have a large above ground outdoor pool. We are used to using chlorine granules from our previous intex pool. That pool did not have a sand filter. This new pool does. Can we use granules with a sand filter?

    • Hi, sure you can, the filter doesn’t change any usage of pool chemicals. Best practice is to pour the granules into a 5-gal bucket filled with water, stir for a minute to dissolve, then pour around the edge of the pool, with the pump running to help circulate. If any stray granules fall in, sweep them around with the pool brush.

  4. My CYA is 70PPM can I just use the shock to maintain my pool if the CYA stays at this level, I am on a private well and don’t want to have to drain and replace if I don’t have to. Chlorine is the most confusing thing all of the other chemicals are pretty straight forward.

    • Hi Michael, you can use pool shock to treat your pool, regular cal hypo shock has no stabilizer. It will be quite inconvenient however, to have to add it so often, so that you don’t create peaks and valleys of chlorination (very high, then very low). If you buy a new chlorine floater (don’t use one previously used for tablets), you can add a lb of shock, and close the vent holes and it will distribute for a few days. Don’t do this on a vinyl pool, as it will damage the liner. Also must be handled carefully, and removed gently before using the pool. If you are able to add pool shock once or twice per day, you can also treat the pool by adding shock twice per day. Try to avoid leaving opened bags of shock around, it could create a safety hazard. If your pool is big enough, use the whole bag, or if not, dilute the entire bag into a very clean bucket of water, or other pour (carefully) into a very clean gallon milk jug, filled full of water (before adding shock). Then you can use the ‘liquid shock’ for a few days, adding a cup or two at a time (wearing safety goggles, gloves and old clothes!)

  5. Thanks! That makes sense. One thing: per Pinch-a-penny, I’ve always used muratic acid to maintain the pH with the salt system. Is that still an option for a chlorine pool, or should I use special pH up/down products instead?

    • Hi, they are the same thing, one is liquid and one is granular, you can use either to control pH. However, tablet chlorine has a lower pH value than salt generated chlorine, and much lower than bleach, so you will likely find that you don’t need to lower the pH as much, when using tablets. Or, you may find that you need to start using pH Up, or soda ash. Give it some time, and you’ll find out.

  6. My salt cell recently stopped working – the salt system is 8 years old – and I can’t afford to replace it right now so I want to run the pool as a chlorine pool. I’ve been adding liquid chlorine from the pool store and would like to know if there is a more cost effective option, i.e. liquid chlorine from somewhere else or chlorine tablets. I’d also like to know what else I need to add to the pool.

    The pool is 11,700 gallons and I live in Florida and it’s been very dry and hot lately.

    • Hi Sandy,

      The salt system could be expensive to replace, so I understand. You can replace the salt system with bleach (liquid chlorine) administered once or twice per day, but this tends to create peaks and valleys in chlorination, unless you have a chlorine pump, which cost about $400, so the next best way is to use trichlor tablets (or sticks, same thing). Buy a floater, aka floating chlorinator and fill it up with 3 or 4 of the 3″ tablets, and when they dissolve, add 3 or 4 more. Use enough tablets to test a consistent 1-2 ppm, at all times of the day and season. You can also install a larger tablet chlorinator into the plumbing system, after the pump and filter, for greater control.

      In addition to maintaining a constant and consistent chlorine level of 1-2 ppm, you also should make sure that your pH level does not go above 7.6, or below 7.2. Most pools gravitate either up or down, so you need to have some pH adjustment chemicals (ph up and ph down) to keep those good. Beyond that, you also want to check and maintain 3 other chemical levels, total alkalinity, calcium hardness and cyanuric acid (stabilizer) levels. But these three are more slow to move, pH and chlorine are fast to change, so need to be checked more often, a few times a week. the other 3 can be checked every month or two, and adjusted if needed.

      For the yellow algae – uh oh! After balancing the water, with a low-ish pH level of 7.2-7.4, shock the pool with 5 gallons of bleach or 5 lbs of shock. Brush the pool hard, add some clarifier, and when the water is clear, replace your filter media (DE grids, sand or cartridge), or at least soak grids/cartridges in a 10:1 water/bleach solution, to kill any traces of yellow algae, which likes to harbor deep in pool filters.

  7. We need a new pool liner. The pool people said ours deteriorated faster beacuse of poor chemical balance. They recommend unstabilized chlorine and a Chlorine dispenser. What is your thought about this?

    • Hi, it is true that certain chemical issues can pull the resilience out of a liner, by removing plasticizers and making the vinyl brittle. A low pH / low alkalinity environment is quite harsh on the pool, and low calcium levels also are not good. High chlorine levels, consistently, with heavy shocking too, is also very harsh on vinyl. He may be recommending unstabilized chlorine because Trichlor tablets are low in pH, and may require occasional pH correction, to keep pH from getting too low. A chlorine feeder or dispenser is a good idea, to avoid peaks and valleys in chlorination, and protect the liner. However, I think regular Trichlor tablets are fine, used in a floater or chlorinator, you just have to check your pH every week, and have some pH Increaser on hand to raise the pH a little bit once per month.

  8. A friend recommended that I keep tabs floating in a floater and ALSO use granules. I shock weekly as well. Is this over kill?

    • It could be overkill, but it depends. The 5 reasons for shocking are 1). to remove organic bacteria and pathogens not killed by the tablets, or 2) to remove chloramines, or 3) to remove algae, or 4) if the water is cloudy or 5) if you forget to put tablets, or dont’ put enough for a hot day. If your water always looks beautiful, and you consistently and constantly have a 1-3 ppm tested chlorine level from your tablets, and your pool filter is not undersized or limping along, and if your pool usage is low to average – you can probably shock once per month. But If you have a poor filter, or only run the pump 8hrs per day, or aren’t vigilant in your daily chlorine level and pH levels, or if you notice algae, cloudy or dull water – then you may need to shock weekly. But if everything looks great, you can shock 1-2x per month. And, you probably don’t need to add granules AND tablets for daily chlorination, just enough tablets to register a consistent 1-3 ppm reading. Too Low? Add another tablet. Too High? Remove 1 or 2 tablets …

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