What Is Cyanuric Acid and How Does It Affect The Chemistry In My Swimming Pool

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What Is Cyanuric Acid and How Does It Affect The Chemistry In My Swimming Pool

With proper chemistry keeping your swimming pool crystal clear is easy.

With proper chemistry keeping your swimming pool crystal clear is easy.

Chlorine is the most important chemical in your swimming pool to keep it clear and free of algae if used appropriately. With that said, the most common chemical used to prevent chlorine loss in swimming pools in cyanuric acid (CYA, stabilizer or conditioner). During the long, hot summer months the sun’s ultraviolet rays destroy free chlorine but having the proper amount of CYA in the swimming pool can prevent this. Knowing that we hope this post helps to explain why CYA is necessary but also what happens when it gets higher than what is considered normal levels.

As explained earlier chlorine is extremely important to have in the swimming pool to prevent algae growth but maintaining proper pH levels, phosphate levels, and calcium hardness levels are also important in maintaining crystal clear water in your swimming pool. The bottom line is, if cyanuric acid is used properly it can reduce the cost of maintaining a swimming pool because it prevents chlorine loss and reduces the amount of chlorine needed to properly sanitize a swimming pool.

With that being said, you are now probably wondering what are considered normal amounts of CYA and what is considered too high? Typically, the ideal amount of CYA is between 30-50 parts per million (ppm) but depending on how much direct sunlight the swimming pool gets, that number could be a little higher. Whereas, when the CYA levels rise above 100ppm, that can cause a fair amount of other problems too. The biggest issue when CYA levels rise above 100ppm is the effectiveness of chlorine because the higher levels tend to bind up the chlorine making it harder to kill algae and other bacteria. When this happens the only way to reduce CYA is to replace the water in the swimming pool.


  1. Shannon says:

    New pool owner. I understand that low CYA levels effect chlorine and the need to keep these levels maintained. I would like to know if low CYA will cause my water to pull the calcium out of my plaster? I thought only a low level of CH would do that. I can’t find a correlation between CYA or stabilizer and CH.

    Back story: had new pool installed with colored plaster in late Dec 2016. CH Jan 19th is 160. CH Jan 26th is 200. In March my plaster became etched with calcium deposit everywhere. Plaster company states after testing water that it’s because my ” stabilizer ” is too low and pulled calcium out of plaster. They had no concerns with any other results. CH was 400 at testing. I have an ozone generator and keep my chlorine level around 1ppm.

    • KenS says:

      Hi Shannon, thanks for the note but you are correct when calcium levels are too low that is when it can be pulled out of the plaster. CYA doesn’t do that. CYA is a stabilizer which works directly with chlorine. That is why they recommend calcium to be between 200 – 400 parts per million. Please let us know if you have any other questions. 🙂

  2. John LaGrandeur says:

    Does Cyanuric acid grab Ca and Mg from the water before it can form an insoluble salt with Cl? I have a salt water pool and after 4 years have high Ca and Mg levels. I think the Ca and Mg grab the Cl coming off my salt generator before it can react with algae. My salt generator (turbo cell) is clogged after several weeks with Ca/Mg Chloride. Now that I use Cyanuric acid, my free Cl is OK and no algae.

    Instead of adding CNA I am thinkin of deionizing my pool with a reverse osmosis truck.

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