Pool Construction
Cyanuric Acid (CYA) Calculator
CYA is sun-block for chlorine. Too little = chlorine burns off in hours. Too much = chlorine becomes useless. Calculate dose or required drain.
CYA targets by chlorine source
- Manual chlorine (cal-hypo, bleach): 30 ppm
- Trichlor tabs or dichlor: 30–50 ppm (these add CYA every dose — watch it climb)
- Salt water generator (SWG): 60–80 ppm (extra CYA protects the cell's chlorine output)
- Indoor pool: 0 ppm — CYA does nothing without UV exposure
FAQ
Can't I just keep adding CYA? +
No — CYA only leaves with water replacement. If your CYA is at 120, you have to drain and refill. There's no chemical that lowers it (some products claim to — most don't work).
Why does high CYA matter? +
High CYA "binds" chlorine — your free Cl looks fine on a test but very little of it is actually active sanitizer. That's why pools with 100+ CYA get algae even at 5 ppm free Cl.
Best way to add CYA? +
Sock-in-skimmer method: tie granular CYA in an old sock, hang in skimmer, run pump 2–3 days. Slow but won't cloud water like dumping it straight in.
How fast does CYA dissolve? +
Slowly — full dissolution can take 4–7 days. Don't re-test for at least a week.