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CYA: The Sunscreen That Can Overstay Its Welcome

Writer: Amanda Lima
Amanda Lima
Oct 15
2 min read

Your chlorine has a sunscreen of its own, and like sunscreen, a little helps while too much can overstay its welcome. For Frisco and North Dallas pool owners, cyanuric acid, or CYA, explains why a pool can test fine on chlorine and still sanitize slowly. In this video, Next Wave Pool Care explains how CYA builds up week after week, the working range to aim for, and the practical way to bring a high level back down.

On a sunny day, CYA shields chlorine from ultraviolet light, so it does not burn away before it can clean the water. But CYA also holds onto chlorine. As the level climbs, less of that chlorine is free to sanitize quickly, even when a test makes the water look fine.

Here is the sneaky part. Stabilized trichlor tablets and dichlor products add a little more CYA every time they dissolve. Chlorine gets used up. CYA does not evaporate or get used up with it, so week after week, the sunscreen layer gets thicker.

The Working Range

For many outdoor chlorine pools, about 30 to 50 parts per million is the working range, and the chlorine target has to rise with CYA, roughly 7.5 percent of the CYA level as a minimum. If CYA gets too high, there is no magic chemical that makes it vanish. The practical fix is to replace some of the pool water with fresh water, then test again.

So do not guess. Know the CYA number before judging the chlorine number. The right amount protects your pool. Too much just slows the cleanup crew down.

Key Takeaways

  • CYA shields chlorine from ultraviolet light so it does not burn away in the sun, but it also holds onto chlorine, so less is free to sanitize quickly as the level climbs.

  • Stabilized trichlor tablets and dichlor products add a little more CYA every time they dissolve, and CYA does not evaporate or get used up, so it builds week after week.

  • For many outdoor chlorine pools, about 30 to 50 parts per million is the working range, and the chlorine target has to rise with CYA, roughly 7.5 percent of the CYA level as a minimum.

  • There is no magic chemical that makes high CYA vanish: the practical fix is to replace some of the pool water with fresh water, then test again.

 
 
 

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