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How to lower cyanuric acid in a pool
Replacing water is the only reliable way. CYA does not evaporate, and ordinary filters do not catch it, so it stays until the water leaves.
How much water to replace
| Current CYA | To 50 ppm | To 40 ppm | To 30 ppm |
|---|---|---|---|
| 60 ppm | 17% | 33% | 50% |
| 80 ppm | 38% | 50% | 63% |
| 100 ppm | 50% | 60% | 70% |
| 120 ppm | 58% | 67% | 75% |
| 150 ppm | 67% | 73% | 80% |
Doing it safely
Do not drain a vinyl pool below the liner's safe level, and do not empty an in-ground pool without advice: ground water can lift the shell. A partial drain over several days is safer, and heavy backwashing also removes some.
Biological CYA reducers exist, but results vary, so test before you count on one. Reverse-osmosis trailers are a real option in dry areas where water is costly, and these can also cut calcium.
Stop it from coming back
Trichlor tablets and dichlor shock are the usual source. Each 1 ppm of chlorine from trichlor adds about 0.6 ppm of CYA, and from dichlor about 0.9 ppm. Switch to liquid chlorine or cal-hypo until your level is back in range.