Raising CYA
Stabilizer doses are simple mass math: amount = ppm change × pool liters ÷ 1,000 ÷ purity. Granular cyanuric acid is close to 100% pure, so 10 ppm in 10,000 gallons is about 13 ounces.
The catch is how slowly it dissolves. A test taken the next day will read low, and adding more at that point is a common way to overshoot. Wait about a week, and don’t backwash in the meantime.
Lowering CYA
Cyanuric acid doesn’t break down in normal pool conditions or evaporate, so it only goes down when water leaves the pool. To lower it, replace water:
fraction to replace = (current − target) ÷ current, assuming your fill water has no CYA.
To go from 100 ppm to 50 ppm, replace half the water. Draining in stages (a third at a time) is safer for many pools.
Match chlorine to your CYA
Whatever CYA you end up with sets the free chlorine you need to keep: about 7.5% of CYA as a minimum, and about 40% to shock. The result shows both for your new level.
Assumptions and limitations
- Granular stabilizer can take up to a week to dissolve and show fully on a test.
- Lowering CYA by dilution assumes your fill water contains no CYA. Test it if you're unsure.
- CYA tests judge cloudiness by eye and are imprecise, especially at low levels. Confirm a surprising result before draining.
Key terms
Common questions
How much stabilizer raises CYA by 10 ppm?
About 13 ounces of pure cyanuric acid per 10,000 gallons.
What is a good CYA level?
For outdoor chlorine pools, 30–50 ppm is widely recommended; salt-generator pools in strong sun often run 60–80 ppm. CDC's public-pool code caps CYA at 90 ppm. Indoor pools need little or none.
Do CYA reducer products work?
Some enzyme-based products have been sold to lower CYA, with mixed real-world results. Replacing water is the method that reliably works, which is why this calculator uses it.
Sources and methodology references
- Model Aquatic Health Code, US Centers for Disease Control and PreventionCYA limit of 90 ppm and minimum free chlorine with stabilizer (public pools).
- Pool School (chlorine/CYA chart), Trouble Free Pool
Published October 2, 2026. Results are estimates. See how our calculators work.
Spotted a wrong result or an outdated source? Report a problem with this calculator.
Related tools
- Chlorine calculatorSee how much chlorine to add to reach the right free chlorine level for your pool's stabilizer, in ounces, gallons or pounds of the product you actually have.
- Pool shock calculatorWork out the shock level your pool actually needs and how much product gets you there. For algae it depends on your stabilizer; for a "chlorine smell" it depends on combined chlorine.
- Salt calculatorFind how much salt to add, in pounds and bags, to reach the level your salt chlorine generator needs.
- Pool opening plannerTurn your first test of the season into an ordered start-up checklist with balancing and chlorine doses filled in.
Related guides
- Cyanuric Acid (Pool Stabilizer): How Much You Need and Why It MattersStabilizer stops sunlight from destroying chlorine, but it also raises the chlorine level your pool needs. How CYA works, good levels, and how to raise or lower it.Read the guide (3 min)
- Pool Water Chemistry for Beginners: What Each Test Number MeansWhat free chlorine, pH, alkalinity, CYA, calcium hardness and combined chlorine actually tell you, which ones matter most, and what order to fix them in.Read the guide (4 min)
- How to Shock a Pool (and How Much Shock You Actually Need)How to shock a pool so it actually works. Find the right chlorine level for your stabilizer, choose a product, and hold the level until the job is done.Read the guide (4 min)
- How to Lower (or Raise) Pool pH SafelyWhy pool pH drifts up, how to bring it down with muriatic or dry acid, how to raise it, and why your alkalinity decides how much acid you actually need.Read the guide (3 min)