How much stabilizer for a 20,000 gallon pool?
A 20,000 gallon pool needs about 6.68 lb (107 oz) of granular stabilizer to take cyanuric acid from 0 to 40 ppm. At 40 ppm, keep free chlorine at least 3 ppm.
How to work it out
- In short: stabilizer is added by weight — the rise you want times the water in your pool.
- Rise: 40 − 0 = 40 ppm
- 40 mg per litre × 75,708 L = 3,028 g of cyanuric acid = 6.68 lb (107 oz)
- Chlorine to keep at 40 ppm CYA: about 3 ppm (Trouble Free Pool’s 7.5% convention; CDC minimum with CYA: 2 ppm)
A 20,000 gallon pool takes a small bucket of stabilizer from scratch. Because it dissolves slowly and only leaves with water, getting the amount right the first time saves a lot of draining later.
Adjust for your project
- CYA rise
- 40 ppm
- Free chlorine to keep at that CYA (7.5% convention)
- 3 ppm
- Per 10 ppm in this pool
- 1.67 lb (26.7 oz)
- Granular stabilizer dissolves slowly — often days. Follow the label (many say the skimmer, a sock, or a bucket), keep the pump running, and don’t backwash for a few days. Test CYA again after the dissolve time; the MAHC asks public pools to retest 24 hours after adding it.
- Stabilized chlorine adds CYA as you go: trichlor tablets about 0.6 ppm per ppm of chlorine, dichlor about 0.9. Using them? Aim lower and let them make up the rest.
Granular stabilizer for 0 → 40 ppm, by pool size
| Pool | Add this much stabilizer | Per 10 ppm in this pool |
|---|---|---|
| 10,000 gal | 3.34 lb (53.4 oz) | 13.4 oz |
| 15,000 gal | 5.01 lb (80.1 oz) | 1.25 lb (20 oz) |
| 20,000 gal | 6.68 lb (107 oz) | 1.67 lb (26.7 oz) |
| 25,000 gal | 8.35 lb (134 oz) | 2.09 lb (33.4 oz) |
| 30,000 gal | 10.01 lb (160 oz) | 2.5 lb (40.1 oz) |
Adding about seven pounds
Each 10 ppm is about 1.67 lb of granular cyanuric acid at this size, so 40 ppm is about 6.7 lb. Granular stabilizer can take several days to dissolve fully, which is the main thing to plan around:
- Split it. Put half in a sock or mesh bag in front of a return (or follow your label), let it dissolve, then the other half. Squeezing the bag daily speeds it up.
- Filter. Don’t backwash or clean a cartridge for several days; undissolved granules caught in the filter go out with the backwash.
- Test after a week. A CYA turbidity test reads in coarse steps; 35 and 45 ppm look much the same.
- Prefer 30 ppm? That is about 5 lb, a sensible start if you plan to use tablets later in the season.
- Going to a salt cell? For 70 ppm it is about 11.7 lb. See what CYA and chlorine a salt water pool needs.
At 40 ppm the pool needs at least 3 ppm of free chlorine by the common 7.5% convention — about 61 fl oz of 12.5% liquid chlorine to raise it from 0 to 3 ppm in this pool, as on how much chlorine for a 20,000 gallon pool. Smaller pool: how much stabilizer for a 10,000 gallon pool.
Different size? Use the full Pool Stabilizer (CYA) Calculator.
What you’ll need
- Stabilizer / conditioner (cyanuric acid)Budget price
Shields chlorine from sunlight. Dissolves slowly — follow the label (many say a skimmer or a sock), and don’t backwash for a few days.
See options on Amazon (opens in a new tab) - FAS-DPD drop test kit (chlorine, pH, TA, CH, CYA)Mid-range price
A drop-count kit reads free chlorine to 0.5 ppm (or 0.2 ppm), plus pH, alkalinity, calcium and stabilizer. Every dose on this site starts from a test, so this is the one thing worth buying first.
See options on Amazon (opens in a new tab) - Liquid pool chlorine (sodium hypochlorite)Budget price
Adds chlorine without stabilizer or calcium. Strength is printed on the label — commonly 10% or 12.5% — and it weakens with age and heat, so buy it fresh.
See options on Amazon (opens in a new tab)
As an Amazon Associate we earn from qualifying purchases. Links to products are affiliate links — they cost you nothing extra and help keep these calculators free.
Frequently asked questions
How much stabilizer for a 20,000 gallon pool to reach 30 ppm?
About 5.01 lb (80.1 oz) of granular cyanuric acid from zero.
How much liquid stabilizer for a 20,000 gallon pool, 0 to 40 ppm?
About 2.5 gal (10 qt) at one label’s rate (4 fl oz per ppm per 10,000 gallons).
How much stabilizer to raise a 20,000 gallon pool from 20 to 40 ppm?
About 3.34 lb (53.4 oz) of granular.
Other common sizes
- How much stabilizer for a 10,000 gallon pool — 2.5 lb (40.1 oz)
Sources
- Leslie’s — Pool Stabilizer (cyanuric acid) label (opens in a new tab) — 100% cyanuric acid; 2-1/2 lb per 10,000 gallons raises CYA by 30 ppm.
- Leslie’s — Instant Pool Water Conditioner Plus (liquid) label (opens in a new tab) — 4 oz in 10,000 gallons raises CYA 1 ppm; 1 gallon raises it 32 ppm per 10,000 gallons.
- CDC — Model Aquatic Health Code, 5th edition (2024), code (opens in a new tab) — Free chlorine minimum 1.0 ppm (2.0 with CYA, 3.0 in spas); pH 7.0–7.8; CYA at or below 90 ppm; CYA:FC above 45:1 is an imminent hazard; TA 60–180 ppm; turnover tables.
- CDC — Model Aquatic Health Code, 5th edition (2024), annex (opens in a new tab) — CYA reduces chlorine’s effectiveness; correcting total alkalinity for CYA by subtracting CYA ÷ 3.
- CDC Healthy Swimming — Home pool and hot tub water treatment and testing (opens in a new tab) — pH 7.0–7.8; free chlorine at least 1 ppm in pools (2 ppm with cyanuric acid) and 3 ppm in hot tubs; no CYA in hot tubs; test twice a day.
- Trouble Free Pool (hobbyist forum wiki) — CYA/chlorine relationship (opens in a new tab) — A widely used hobbyist convention, not an official standard: minimum FC 7.5% of CYA, SLAM (shock) level 40% of CYA, salt-water pools 5%.
- ICC Building Safety Journal (PHTA Recreational Water Quality Committee) — Trichlor: the dependable pool performer (opens in a new tab) — Trichlor is 90% available chlorine and adds 0.6 ppm cyanuric acid for each ppm of chlorine.
- CDC — Pool chemical injuries press release (2014) (opens in a new tab) — Never mix pool chemicals, especially chlorine products with acid; add chemical to water, never water to chemical.