Pool stabilizer calculator
Cyanuric acid protects chlorine from the sun, but too much makes chlorine sluggish. Work out how much to add, or how much water to swap out.
Add stabilizer
- Put the granules in a nylon sock hung in front of a return, or in the skimmer basket with the pump running 24/7.
- Don’t backwash or clean the filter for 5–7 days.
- Test after a week. Readings taken earlier will be low.
Chemical safety: read the product label first and follow it where it differs from this page. Add acid to water, never water to acid. Never mix chlorine products with acid or with each other, not even in a bucket. Add one chemical at a time with the pump running, wait at least 30 minutes (acid and chlorine: until the next test), and retest before topping up.
Where stabilizer comes from
Besides bags of stabilizer, every trichlor tablet and dichlor dose adds some: about 0.6 ppm CYA per ppm of chlorine from trichlor, and 0.9 ppm from dichlor. A pool fed only on tabs can gain 30–50 ppm of CYA in a season. See the chlorine calculator for how the FC target rises with CYA.
Questions pool owners ask
How much stabilizer do I add to my pool?
About 13 oz of cyanuric acid raises CYA by 10 ppm in 10,000 gallons. To go from 0 to 40 ppm in 15,000 gallons you need about 5 lb. Liquid stabilizers are weaker per pound; follow their label.
What should my stabilizer (CYA) level be?
For outdoor chlorine pools, 30–50 ppm is the common target; salt pools often run 60–80 ppm per salt-cell manufacturers. CDC recommends not using stabilizer in hot tubs, and many health codes cap public pools at 90–100 ppm.
How do I lower cyanuric acid?
Replace water. CYA doesn’t break down meaningfully in a chlorinated pool, so partial drain and refill is the dependable method. The calculator shows what share to replace, assuming your fill water has little or no CYA.
Why does stabilizer take so long to show up?
Granular cyanuric acid dissolves very slowly, often 2–7 days. Put it in a sock or skimmer basket with the pump running, don’t backwash or clean the filter for a week, and only retest after that.
Is too much stabilizer bad?
High CYA doesn’t stop chlorine working completely, but it means you must hold much higher free chlorine to get the same sanitizing power (about 7.5% of CYA as a minimum). Above 80–100 ppm that becomes expensive and algae outbreaks get harder to clear.