Cyanuric acid (CYA) calculator
Updated:
Cyanuric acid is sunscreen for your chlorine. Enter your current and target CYA and pool volume to get the exact amount of stabilizer to add.
How much stabilizer to add?
About 13 oz of cyanuric acid per 10,000 gallons raises CYA by about 10 ppm, and the calculator scales it to your volume. It dissolves slowly. Trouble Free Pool’s checklist has you put it in a sock hung in front of a return instead of pouring it in. Re-test once it has fully dissolved, before adding more.
Why CYA matters
The MAHC Annex describes CYA as effective at protecting chlorine from breakdown by sunlight. The cost is that CYA binds chlorine and slows how fast it kills germs, so the free chlorine you need rises with it. Trouble Free Pool’s chart puts the minimum at 7.5% of your CYA.
CYA too high?
No chemical removes CYA, so the fix is dilution: replace part of the water, and the calculator gives the percentage. The MAHC caps CYA at 90 ppm for public pools and requires them to close at 300 ppm until it is brought down (5.7.3.1.3.2 and 5.7.3.1.3.3). Going forward, liquid chlorine and cal-hypo add no CYA, while trichlor and dichlor add it with every dose.
Hot tubs should not use CYA
The CDC recommends against cyanuric acid or stabilized chlorine in hot tubs, and the MAHC phases it out of public spas (5.7.3.1.3.1). Keep a hot tub on unstabilized chlorine at 3 ppm or more, or on bromine.
How the dose is calculated
Raising and lowering CYA are both simple.
Raising CYA
grams = 0.00378541 × (target − current) × gallons
The calculator treats stabilizer as pure cyanuric acid, so the plain ppm-to-grams constant applies. For 10 ppm in 10,000 gallons that is 379 g, about 13 oz.
Lowering CYA
share of water to replace = 1 − target ÷ current
Halving CYA means replacing half the water.
Ideal ranges
| Level | Target | Notes |
|---|---|---|
| Public pool maximum | 90 ppm | MAHC 5.7.3.1.3.2; close at 300 ppm or more |
| Hayward and Pentair manuals | 30–50 ppm | Chlorine and salt pools; the range the app uses |
| Liquid chlorine pool | 30–60 ppm | TFP |
| Salt pool | 60–90 ppm | TFP |
| Hot tub / spa | None | CDC recommends no CYA in hot tubs |
Frequently asked questions
Is CYA the same as conditioner or stabilizer?
Yes. Cyanuric acid, stabilizer, and conditioner are the same thing.
Why is my chlorine demand so high?
Very high CYA can make chlorine seem to stop working, which pool stores call chlorine lock. The chlorine is still there, mostly bound to CYA. Confirm the reading, dilute to bring CYA back into range, and keep free chlorine at the minimum for the CYA that remains.
Can I use stabilizer in a hot tub?
The CDC recommends against it. Use unstabilized chlorine at 3 ppm or more, or bromine.
Sources
- CDC, Model Aquatic Health Code, 5th edition (2024), Code Language. Sections 5.7.3.1.3.1 to 5.7.3.1.3.3: CYA in spas, the 90 ppm cap and the 300 ppm closure
- CDC, Model Aquatic Health Code, 5th edition (2024), Annex. Section 5.7.3.1.3.1: sunlight protection and slower disinfection
- CDC, Home Pool and Hot Tub Water Treatment and Testing (May 10, 2024). No CYA in hot tubs
- Trouble Free Pool, CYA Chlorine Relationship (Chlorine/CYA chart). Minimum free chlorine as 7.5% of CYA
- Trouble Free Pool, Pool Chemical Levels: Pool Industry vs TFP (December 21, 2025). CYA targets for liquid chlorine and salt pools
- Trouble Free Pool, SLAM Process Checklist (V2). Adding stabilizer in a sock
- Hayward, AquaRite 900 Series Electronic Chlorine Generator manual (092623 Rev D). Stabilizer 30–50 ppm
- Pentair, IntelliChlor IC15/IC20/IC40/IC60 Installation and User’s Guide (P/N 520589 Rev. R, 2023). Cyanuric acid 30–50 ppm
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