What Is Cyanuric Acid or Chlorine Pool Stabilizer?

Most pool owners add cyanuric acid to their swimming pool every year, but do they REALLY know what it is and what it does? It’s actually a pretty common chemical that only needs to be added once at the beginning of each season, or depending on your pool, sometimes not at all.

What Is Cyanuric Acid or Chlorine Stabilizer?

Cyanuric Acid, otherwise known as Chlorine Pool Stabilizer or Conditioner, is what protects your chlorine from being eaten away by the sun’s ultraviolet rays. The sun can eat up to 1 ppm (part per million) of chlorine every hour if it’s not protected.

Most chlorine that you find in tablet, stick or granular form, have cyanuric acid as an ingredient, which is why you only need to add it at the beginning of the year.

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After that, every time you add chlorine to your pool, you’ll be keeping your levels of cyanuric acid in check. Be sure to keep an eye on these readings throughout the year. I recommend keeping it around 50 PPM.

Chlorine tablets, sticks and granular are known as Cyanurates, which basically means they contain cynauric acid as an ingredient. Make sure, when you’re buying chlorine, to look out for chlorine tablets, sticks and granular made with calcium hypochlorite. Calcium hypochlorite is the active ingredient in chlorine based shock and it does not contain cyanuric acid.

Testing For Cyanuric Acid

You can buy test strips that include cyanuric acid readings on them or you can buy a separate liquid test kit that has it. These are usually kind of expensive though. Since you really don’t have to keep a close eye on these readings, it’s best to just take a sample of your water to your local pool store that offers free water testing and just have them check it there every once in a while.

When Should You Add Pool Stabilizer (CYA)?

Because most chlorine contains small amounts of cyanuric acid, you only have to add it about once at the beginning of the year to set it up. Once you have a good base of cyanuric acid in your pool, each time you add chlorine, it should keep it regulated throughout the year. However, if you have a to drain a large amount water out of your pool for any reason throughout the year, you may need to add more to bring your levels back to normal.

How To Add Cyanuric Acid

Cyanuric acid can be tricky to add to your swimming pool. Some chemical companies will tell you to dissolve it in a bucket of water. Keep in mind that Cyanuric acid dissolves very slowly. Other companies will tell you to add it directly to the pool. I would recommend dissolving it in a bucket of water, no matter what. Cyanuric acid is in fact, an ACID, so adding it to your liner pool and having those slow dissolving acidic granular sitting on your liner is not really a great idea.

NOTE: Whatever you decide, do not add cyanuric acid through the skimmer and through the filter. In fact, don’t add any chemicals that way!

Cyanuric acid is a very important chemical when it comes to good pool care. It allows you to maintain a healthy chlorine reading without constantly adding chlorine to your pool. Those hot summer days can really wreak havoc on your pool’s chlorine reading. Be sure to keep your levels in check this season.

Happy Swimming!

What Is Cyanuric Acid or Chlorine Stabilizer?

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  • Great value-added content, Matt! I’ve shared your article with my facebook friends.

  • hangnail

    My 25,000 gal in ground pool has a Cyanuirc Acid level is 63ppm. Do I need to get the level down? If so how? My pool company never mentioned anything. I just noticed it on my printouts.

  • @Hangnail That level should be fine. In order to bring it down, you would need to dilute your pool with fresh water.

  • Bj Crawford

    Why shouldn’t I add chemicals through the skimmer?

  • Matt Giovanisci

    Because adding a concentration of chemicals through your system is bad according to people in the industry. I haven’t read any official studies, but that seems to be the consensus.

    Really, you shouldn’t add shock through the skimmer if you have a chlorinator because you can literally blow up your chlorinator and people can get hurt. Tri-chlor and Calcium Hypochlorite create a dangerous gas.

  • Mommyofthreeboys

    I just added CYA and I put it in a pantyhose knee-hi. I bought 4 plus sized ones for $1.29 at Walgreens. I needed to add 2 lbs of the acid. I added it to the knee-hi, tied the top, and added it to my skimmer. I gently squeezed the stocking a few times and left it for about an hour. I went back out and squeezed the knee-hi and it it did dissolve within 15 minutes. I rinsed out the knee-hi hung it to dry and will use it next time. I left my pump running for 24 hours also after adding it. My Cl levels and CYA levels were perfect the next morning and my pool is as clear as a bell. Before adding it my Cl levels were really low, CYA was low and the water was slightly cloudy. Get the pantyhose it works great and you won’t have granules going through that filter or pump.

  • Matt Giovanisci

    Great tip! Thanks :-)

  • Montie L. Manning

    First off, Matt I love, love, love your site! You are now my “go to” source on all things pool related. I have questions about CYA. I have a 22,000 gallon in ground pool with a vinyl liner. According to my home test kit, my CYA is well above 100, basically off the charts. So my questions:

    1. Are levels this high harmful to swimmers? Filter? Heater? Liner?
    2. What should my free chlorine target be?
    3. Can I get by this season with CYA this high and address the issue at the end of season by draining and refilling the pool?
    4. Does CYA affect my PH, alkalinity, etc.?
    5. Should I only use unstabilized chlorine products given the high CYA level? If so, any good recommendations?

    Thanks in advance!

  • Matt Giovanisci

    Not harmful no. Free chlorine should be between 1 and 3 ppm. High CYA can cause balancing issues with other chemicals. Correct it. Use stabilized chlorine. It will help maintain CYA levels when you get them to the correct level.

  • Montie L. Manning

    Thanks Matt! Had a water sample tested at Leslie’s. According to it, CYA is 80. Their test shows everything is ok, except phosphates are high measuring at 200.