Pool CYA / Stabilizer Calculator

Cyanuric acid reduces sunlight-driven chlorine loss, but it also changes chlorine availability. Higher measured CYA requires an appropriate higher FC target. CYA does not replace adequate chlorine or regular testing.

For an outdoor manually chlorinated pool, 30–50 ppm is a common operating target. Salt generators have model-specific instructions; use the manual to choose the target. This tool accepts targets through 80 ppm as a conservative management limit, including 80. Indoor pools generally do not need stabilizer.

No. Chlorine availability changes continuously with the FC/CYA relationship. The tool’s 80 ppm addition ceiling is an operating choice, not a chemical cliff. Above it, stop adding stabilizer and assess FC requirements, measurement accuracy and an appropriate water-exchange plan.

Water exchange with lower-CYA replacement water reduces concentration. If replacement water has zero CYA, exchanging two thirds of the original water would reduce 120 ppm to 40 ppm in an ideal replacement; simultaneous mixing requires more. This arithmetic is not permission to drain. Pool construction, liner support and groundwater must be assessed before lowering water. Use a qualified professional’s exchange plan.

Wait at least seven days after the first staged addition, or longer as the label/test instructions require, then obtain a fresh reading and recalculate. Do not add the original remainder automatically. Trichlor and dichlor also add CYA; account for those sources.