Pool Water Dilution Calculator
Reviewed by Hamza Gujjar, Algorithm Architect & Software Developer
Last updated: July 27, 2026The one pool chemistry problem you can't fix with chemicals
Almost every pool chemistry imbalance can be corrected by adding the right chemical - except excess cyanuric acid. CYA does not break down, evaporate, or filter out on its own, so the only way to lower it is diluting the pool with water that contains none.
Worked example
For a pool currently at 120 ppm CYA, targeting 40 ppm:
Dilution = ((120-40)/120) x 100 = 66.7% water replacement needed
This percentage applies to the pool's total volume - for a 20,000-gallon pool, that means draining and refilling roughly 13,340 gallons. Drain partially, refill, retest, and repeat if needed rather than assuming one large dilution will land exactly on target, since refill water itself may carry a small amount of CYA depending on the source.