Cyanuric Acid Calculator
Calculate how much cyanuric acid (CYA) stabilizer to add to your pool, or find out how much water to drain if your CYA is too high.
Cyanuric Acid Needed
Cyanuric Acid (Stabilizer)
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Based on cyanuric acid product at 98% purity. Place CYA in a skimmer basket or sock — never add directly to pool water. Retest after 48 hours.
CYA Too High — Drain Required
Understanding Cyanuric Acid (Pool Stabilizer)
Cyanuric acid (CYA) is a pool stabilizer that shields chlorine from the sun's UV rays. Without it, sunlight can destroy up to 90% of your pool's chlorine within two hours. With proper CYA levels, chlorine lasts much longer, saving you money and keeping your pool safe.
Ideal CYA Levels
- Regular chlorine pools: 30–50 ppm — this range provides good UV protection while keeping chlorine effective. A target of 40 ppm is ideal for most pools.
- Saltwater pools: 70–80 ppm — saltwater generators benefit from slightly higher CYA levels to protect the chlorine they produce. A target of 75 ppm is recommended.
- Above 80 ppm: Chlorine lock — when CYA gets too high, it binds so tightly to chlorine that the chlorine can no longer sanitize effectively, even at high free chlorine readings.
The Dosing Formula
To calculate how much cyanuric acid to add:
lbs of CYA = (Pool Gallons × PPM Increase) ÷ 1,000,000 × 8.34 ÷ 0.98
As a rule of thumb, 1 pound of cyanuric acid raises 10,000 gallons by approximately 12 ppm.
How to Add CYA to Your Pool
- CYA dissolves slowly — place it in a skimmer basket or a mesh sock hung in front of a return jet. Never add it directly to the pool water.
- Allow 48 hours for full dissolution before retesting your CYA level.
- Add CYA in stages if you need a large increase — add half, wait 48 hours, retest, then add more if needed.
Lowering CYA
CYA does not break down, evaporate, or get filtered out. The only reliable ways to lower it are:
- Drain and refill — partially drain your pool and replace with fresh water. This dilutes the CYA proportionally.
- Rain dilution — heavy rainfall naturally dilutes CYA over time, but this is slow and unreliable.
CYA from Chlorine Tablets
Dichlor and trichlor — the most common chlorine products — contain cyanuric acid. Every time you add them, your CYA level creeps up. If you use tablets as your primary sanitizer, monitor CYA monthly. Many pool owners switch to liquid chlorine (which contains no CYA) once their stabilizer level reaches the ideal range.