How much stabilizer for a 20,000 gallon pool

In a 20,000 gallon pool, 1.7 lb (765 g) of stabilizer granules raises cyanuric acid (CYA) by 10 ppm. Taking fresh water from 0 to 40 ppm needs 6.7 lb (3.1 kg). Liquid stabilizer is weaker by weight: 0.63 gal per 10 ppm.

Stabilizer doses for 20,000 gallons

20,000 US gallons (75,708 L).
Change	Granules (99%)	Liquid (25%)
Raise 10 ppm	1.7 lb	0.63 gal
Raise 20 ppm	3.4 lb	1.3 gal
Raise 30 ppm	5.1 lb	1.9 gal
Raise 40 ppm	6.7 lb	2.5 gal
Raise 50 ppm	8.4 lb	3.1 gal
CYA 40 → 70 (salt pool)	5.1 lb	1.9 gal

Run it with your numbers

Add

6.7lb

of Stabilizer granules (cyanuric acid 99%)

108 oz3.1 kg

Raises CYA from 0 ppm to 40 ppm in 20,000 gal.

This is a large change. Add it in stages and retest between them.
Also raises cyanuric acid (stabilizer). It only comes down by replacing water.
Put the granules in a sock in the skimmer basket or in front of a return. Do not backwash for a week.
Stabilizer takes several days to dissolve and register on a test. Do not add more in the meantime.
At CYA 40 your free chlorine minimum becomes 3 ppm and the target 6 ppm.
Adding too much is hard to undo: only draining lowers CYA. If unsure, add three quarters, wait a week and retest.

Check the product label. Strengths vary by brand, so enter the % printed on yours. Add one chemical at a time, into the water, and never mix chemicals.

Save this test and get reminded when it is time to retest.

Pool Calc for iPhoneComing soon to the App Store

About stabilizer

Granules dissolve slowly. Put them in a sock or the skimmer basket with the pump running, and don’t backwash for a week. CYA takes several days to show fully on a test, so don’t top it up before then.

Overshooting is the expensive mistake: nothing you can add lowers CYA, only replacing water does. If you are unsure of your volume, add three quarters of the dose, wait a week and retest.

Manual chlorine pools usually run CYA 30 to 50. Salt water pools run 60 to 80, because the cell makes chlorine all day. Your chlorine target rises with CYA: see the FC/CYA calculator.

Dosing a 20,000 gallon pool

That is about the size of a 30 ft round × 52 in above-ground pool (about 20,270 gal), or a 16 × 32 ft in-ground pool averaging 5 ft deep (about 19,150 gal). 20,000 gallons is a typical backyard pool. Measure the volume once rather than trusting the builder’s brochure: an error of 20% in gallons makes every dose 20% off. The pool volume calculator takes a minute.

Questions

How much stabilizer for a 20,000 gallon pool?

1.7 lb of granular cyanuric acid per 10 ppm. From 0 to 40 ppm: 6.7 lb.

How long does stabilizer take to dissolve?

Granules can take several days to a week to dissolve and register on a test. Wait a week before adding more.

How do I lower stabilizer if I add too much?

Only by replacing water. The drain and refill calculator shows how much.