Stabilizer (CYA) & Shock Calculator
Two closely related jobs in one tool. Use Raise CYA to work out how much stabilizer to add so the sun stops burning off your chlorine, or How much shock? to size a breakpoint shock dose from your chlorine readings.
Aim for about 30–50 ppm CYA in most pools (60–80 ppm for saltwater). Stabilizer dissolves slowly — add it in a sock in the skimmer and don't backwash for a few days.
Enter your pool volume and CYA levels.
About cyanuric acid (stabilizer)
Cyanuric acid (CYA) is sunscreen for your chlorine. Without it, UV light destroys free chlorine within hours; with it, chlorine lasts far longer. Most pools want about 30–50 ppm, and saltwater pools a bit higher at 60–80 ppm. It dissolves slowly, so add it through a sock in the skimmer and avoid backwashing for a few days. You can only lower CYA by diluting with fresh water.
- CYA needed (oz) ≈ gallons ÷ 10,000 × (target − current) ppm × 1.3
About shocking to breakpoint
“Breakpoint” is the point where you've added enough chlorine to fully burn off combined chlorine (the stuff that causes the harsh smell and irritation). The rule of thumb is to raise free chlorine to about 10× your combined chlorine reading, and at least 10 ppm. Not sure of your volume? Use the Pool Volume Calculator first, and see the chlorine guide for step-by-step shocking. New to these terms? The Pool School glossary explains them.