Pool CYA / Stabilizer Calculator

Cyanuric acid (CYA), also called stabilizer or conditioner, protects free chlorine from UV sunlight degradation. Without CYA, sunlight can destroy up to 90% of free chlorine within 2 hours. At 30–50 ppm CYA, chlorine loss to UV is reduced dramatically, improving efficiency and reducing chemical costs in outdoor pools.

For outdoor chlorine pools, the ideal CYA range is 30–50 ppm. For saltwater pools (SWG), 60–80 ppm is often recommended since the generator produces chlorine continuously and benefits from stronger UV protection. Indoor pools do not need CYA since there is no UV exposure. Target 0–20 ppm indoors.

80 ppm is considered the danger threshold for most pools. Above 80 ppm, CYA so strongly bonds to chlorine that even a high FC reading may provide inadequate sanitation. This is called "chlorine lock." The minimum safe free chlorine level rises with CYA (roughly FC = 7.5% of CYA). Many health departments cap CYA at 100 ppm for commercial pools. If CYA exceeds 100 ppm, a partial drain and refill is the only remedy.

The only reliable way to lower CYA is a partial drain and refill with fresh water. There is no chemical that effectively removes CYA. To calculate how much to drain: if CYA is 120 ppm and the target is 40 ppm, you need to replace approximately 67% of the water. CYA dilutes proportionally with water volume. Some CYA-degrading enzyme products exist but results are inconsistent.

Yes. Both trichlor tablets and dichlor granules contain CYA bonded to the chlorine molecule. Each 10 oz of trichlor adds about 6 ppm of CYA to a 10,000-gallon pool. Using tablets as your only chlorine source will raise CYA by 20–30 ppm or more per season. When CYA exceeds 50 ppm, switch to an unstabilized chlorine source (liquid chlorine or cal-hypo) to stop CYA accumulation.