CYA Calculator: How Much Stabilizer Does Your Pool Need?

Cyanuric acid (stabilizer) is sunscreen for your chlorine — too little and the sun destroys your chlorine daily, too much and it locks the chlorine up. The right amount is around 30–50 ppm, and the calculator above sizes the dose to reach it from your current level.

What it calculates

Enter your pool volume and current CYA reading, and the tool estimates how much stabilizer to add to reach the target range. Accurate volume matters as always. If your CYA is already at or above range, the answer is to add none — and if it's well over 50 ppm, the tool can't lower it, because the only practical way down is dilution with fresh water.

Why the range matters both ways

Stabilizer is a Goldilocks number. Below about 30 ppm, an outdoor pool's chlorine burns off fast in sunlight, so you fight chronically low chlorine no matter how much you add. Above about 50 ppm, CYA starts binding chlorine so it can't sanitize effectively — the counterintuitive cause of a green pool with a "normal" chlorine reading. The 30–50 ppm band keeps chlorine both protected and active.

Add slowly, it dissolves slowly

Stabilizer takes time. Add the calculated amount per the product's method (often via the skimmer or by pre-dissolving), run the pump, and give it a day or more to fully register before retesting — CYA is slow to dissolve and read. Add conservatively; since lowering CYA requires draining water, it's better to under-add and top up than to overshoot into the range where chlorine stops working.