How to lower cyanuric acid (CYA)
Updated:
Nothing you can pour in removes cyanuric acid. The only reliable fix is dilution: replace part of your water with fresh. The good news is the math is simple — to halve your CYA, replace half your water.
Step by step
- Confirm the reading before you drainCYA test kits are the least precise in the kit, and the turbidity test is easy to misread. Re-test, ideally with a fresh reagent, before you dump thousands of gallons.
- Work out how much water to replaceThe percentage of water you replace is the percentage CYA drops. CYA 100 down to CYA 50 means replacing half. The CYA calculator does this for your volume.
- Drain and refill in stagesNever fully drain an in-ground pool — a vinyl liner can float and a plaster shell can pop out of the ground under hydrostatic pressure. Drain partway, refill, and repeat if needed.
- Re-balance after refillingFresh fill water resets everything, not just CYA. Re-test and rebalance calcium, alkalinity, pH, and salt after the refill.
- Stop it climbing againTrichlor tablets and dichlor add CYA with every single dose — that is almost always what pushed it up. Switch routine chlorination to liquid chlorine or cal-hypo, which add none.
FAQ
Does anything actually remove cyanuric acid?
Not dependably. Enzyme-based "CYA reducers" give inconsistent results, and reverse-osmosis mobile service works but is expensive and only available in some regions. Partial drain and refill is the standard fix.
What CYA level is too high?
Above about 80-90 ppm in a chlorine pool the free chlorine you need to stay ahead of algae becomes impractical to hold. Above 100 ppm, dilute.
Does CYA go down on its own?
Slowly, through splash-out, backwashing, and rain overflow diluting the pool. In a well-sealed pool with a cover it can sit high for years.
Is high CYA the same as chlorine lock?
It is what people usually mean by it. Chlorine is still present but heavily bound to CYA, so it tests fine and sanitizes poorly. Diluting restores its bite.
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