Cyanuric acid (CYA) stabilizes chlorine against sunlight. Like salt, it’s dosed by the ppm shortfall and volume — and can only be lowered by dilution, so don’t overshoot.
The example
20,000 gal, 20 → 50 ppm.
| A | B | |
|---|---|---|
| 1 | Item | Value |
| 2 | (50−20)×20000/120000 | — |
| 3 | Stabilizer | → ~5 lb |
The formula
The formula:
How it works
How it works:
- CYA gap = target − current; MAX(…, 0) since you can’t add negative.
- Multiply by gallons and divide by the constant (~120,000 for lb/ppm).
- CYA dissolves slowly — add via the skimmer sock and allow days; retest before re-dosing.
- Too-high CYA weakens chlorine; the only fix is dilution.
Educational use only — not chemical-safety or professional advice. Pool chemical dosing varies by product strength, water chemistry, and local rules. Always follow the product label, add chemicals to water (never water to chemical), test before and after, and never mix chemicals. Verify with a professional.
Try it: interactive demo
Gallons, current CYA, target CYA.
Variations
In ounces
Pounds × 16:
Over target?
Dilute to lower:
Dilution fraction
Drain & refill share:
Pitfalls & errors
Dissolves slowly. Add via sock, wait days, retest before more.
Floor at zero. You can’t add negative stabilizer.
Overshoot = dilute. High CYA only comes down by water replacement.
Practice workbook
Frequently asked questions
How do I calculate stabilizer (CYA) to add in Excel?
How do I lower high CYA?
How fast does CYA dissolve?
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