How the stabilizer dose is worked out
oz of stabilizer = (target − current) ÷ 10 × 13 × gallons ÷ 10,000
13 oz of granular stabilizer (cyanuric acid) raises CYA by 10 ppm in 10,000 gallons. A 15,000-gallon pool from 30 to 50 ppm needs 39 oz, just under 2.5 lb; a 10,000-gallon pool filled with fresh water needs 52 oz to reach 40 ppm. Put the granules in a sock or mesh bag in the skimmer basket or in front of a return with the pump running, and do not backwash for a few days.
Why the level matters
Stabilizer shields chlorine from sunlight, but it also slows it down, so the free chlorine you need rises with it: about 7.5 % of the CYA level, or 3 ppm at 40 ppm CYA. Set that with the pool chlorine calculator, and use the pool shock calculator for the shock level, which also follows CYA. Stabilizer only leaves the water by splash-out, backwashing and draining, so the fix for too much is replacing part of the water; the fill time calculator tells you how long the refill takes.
Stabilizer factor (13 oz per 10 ppm per 10,000 gal) and the 7.5 % chlorine rule: Trouble Free Pool, Pool School "Pool Math" and product labels. Read October 18, 2026.
Frequently asked questions
How do I know how much stabilizer to put in my pool?
Test your CYA first, then use (target − current) ÷ 10 × 13 oz × gallons ÷ 10,000. A 15,000-gallon pool from 30 to 50 ppm needs 39 oz. Add it, give it a week to dissolve and register, then retest before adding more.
How many pounds of stabilizer for a 20,000 gallon pool?
From fresh water to 40 ppm: 104 oz, which is 6.5 lb. From 20 to 50 ppm: 78 oz, just under 5 lb. Each 10 ppm takes 26 oz (1.6 lb) in 20,000 gallons.
Can you put too much stabilizer in a pool?
Yes. CYA does not break down or evaporate, and every trichlor or dichlor dose adds more. A high level means you need more free chlorine to stop algae, about 7.5 % of the CYA. Past 80 ppm the usual fix is to replace part of the water; the calculator shows the share.
What is the ideal stabilizer level in a pool?
For a chlorine pool 30 to 50 ppm is common. Salt pools usually run higher, often 60 to 80 ppm, because the cell makes chlorine all day in the sun; follow your chlorinator's manual. Indoor pools out of the sun need little or none.
How long does stabilizer take to dissolve?
Granular stabilizer dissolves slowly and can take up to a week to show fully in a test, so a reading the next day comes out low. Keep it in a sock in the skimmer basket or in front of a return, run the pump, skip backwashing for a few days and retest after a week.