Pool CYA (Cyanuric Acid) Levels Chart
Quick Answer
Ideal cyanuric acid (CYA or stabilizer) for outdoor pools is 30–50 ppm. CYA protects chlorine from UV degradation. Above 100 ppm, CYA locks up chlorine and makes it largely ineffective — a condition called "chlorine lock." The only remedy for very high CYA is dilution.
- CYA 30–50 ppm is the standard for outdoor chlorine pools
- Below 20 ppm: FC degrades in direct sunlight within hours
- Above 80 ppm: chlorine effectiveness drops significantly
- Above 100 ppm: partial drain and refill is the only fix
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Reference table
| CYA level | Status | Effect on chlorine | Action |
|---|---|---|---|
| 0–20 ppm | Too low | FC lost to UV in hours | Add stabilizer (cyanuric acid granules) |
| 20–30 ppm | Low | Moderate UV protection | Add stabilizer if outdoor pool |
| 30–50 ppm | Ideal | Good UV protection | None — maintain range |
| 50–80 ppm | Acceptable | Slight reduction in effectiveness | Monitor; avoid adding more stabilizer |
| 80–100 ppm | High | Noticeable chlorine lock | Partial drain (20–30%) and refill |
| > 100 ppm | Chlorine lock | FC mostly inactive | Drain 30–50% and refill; rebalance |
Frequently Asked Questions
What is CYA in a pool?
CYA stands for cyanuric acid, also called stabilizer or conditioner. It bonds loosely with free chlorine and protects it from being destroyed by ultraviolet light. Outdoor pools need 30–50 ppm CYA; indoor pools typically need none.
What happens if CYA is too high?
Above 80–100 ppm, CYA over-stabilizes chlorine so that it cannot oxidize bacteria and algae effectively. This is sometimes called "chlorine lock." Adding more chlorine will not help. The only fix is dilution — partial drain and refill.
How do I raise CYA in my pool?
Add granular cyanuric acid (stabilizer) through the skimmer or in a stocking held in front of a return jet. It dissolves slowly — allow 24–48 hours and retest. Add incrementally to avoid overshoot.
Do salt water pools need CYA?
Yes. Salt water chlorine generators produce unstabilized chlorine (same as liquid chlorine) that degrades rapidly in sunlight. Most SWG pools run CYA at 60–80 ppm for efficient generator performance.
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Also see: Pool Chemical Levels Chart · Chlorine Levels Chart
Last updated: June 2026