In an 18,000 gallon pool with alkalinity 80, about 15 fl oz (442 mL) of 31.45% muriatic acid lowers pH from 7.8 to 7.5. Acid demand rises with alkalinity, so use the calculator below with your TA. For alkalinity, 0.36 gal (1.4 L) lowers TA by 10 ppm.
| Change | 31.45% acid | 14.5% acid |
|---|---|---|
| pH 7.8 → 7.5 | 15 fl oz | 0.27 gal |
| pH 8.0 → 7.5 | 21 fl oz | 0.39 gal |
| pH 8.2 → 7.6 | 20 fl oz | 0.37 gal |
| pH 7.7 → 7.4 | 18 fl oz | 0.33 gal |
| Lower alkalinity | 31.45% acid | 14.5% acid |
|---|---|---|
| TA −10 ppm | 0.36 gal | 0.85 gal |
| TA −20 ppm | 0.72 gal (2 parts) | 1.7 gal |
| TA −30 ppm | 1.1 gal (3 parts) | 2.5 gal |
Add
15fl oz
of Muriatic acid 31.45%
1.9 cups438 mL
Lowers pH from 7.8 to 7.5 in 18,000 gal at TA 80. TA afterwards: about 77 ppm.
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 StoreWear goggles and gloves, open the jug outdoors and stand upwind. With the pump running, pour the acid slowly in front of a return jet, low over the water. Always add acid to water, never water to acid.
Keep each addition to about 0.45 gal in this pool (12.5 ppm of alkalinity), then let it circulate for 30 minutes and retest pH. Bigger single doses can etch plaster and damage equipment near the return.
Never add acid and chlorine at the same time or in the same spot. Mixing them releases chlorine gas.
That is about the size of a 27 ft round × 54 in above-ground pool (about 17,130 gal), or a 16 × 32 ft in-ground pool averaging 5 ft deep (about 19,150 gal), or a 15 × 30 ft in-ground pool averaging 5 ft deep (about 16,830 gal). 18,000 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.
To lower pH from 7.8 to 7.5 at TA 80, about 15 fl oz of 31.45% acid. To lower alkalinity by 10 ppm, 0.36 gal.
Wait until it has circulated, typically about 30 minutes with the pump running, and retest pH before swimming. Keep children and pets out of the water until pH is back in range.
Yes. It is the same acid at about half the strength, so you need roughly twice as much: 0.85 gal lowers TA 10 ppm in 18,000 gallons.