Muriatic acid to lower pH
fl oz = (pH now − target) ÷ 0.4 × 26 × gallons ÷ 10,000 × TA ÷ 100 × 31.45 ÷ strength
About 26 fl oz of 31.45 % muriatic acid lowers 10,000 gallons from pH 7.8 to 7.4 at a total alkalinity of 100 ppm. A 20,000-gallon pool from 8.0 to 7.5 at the same alkalinity needs 65 fl oz, about half a gallon. Weaker acid needs more: multiply by 31.45 and divide by the percentage on your jug.
Muriatic acid to lower total alkalinity
fl oz = (TA now − target) ÷ 10 × 25.6 × gallons ÷ 10,000 × 31.45 ÷ strength
About 25.6 fl oz of 31.45 % acid lowers total alkalinity by 10 ppm in 10,000 gallons. The acid lowers pH at the same time, so the usual method is to add acid, let pH drop to about 7.2, aerate (jets pointed up, a waterfall) until pH climbs back, and repeat. Alkalinity stays down while pH comes back up. The pool alkalinity calculator gives the baking soda dose if you overshoot, and the pool pH calculator covers raising pH with soda ash.
Adding it safely
Wear gloves and eye protection and work outdoors. Pour the acid slowly into the deep end in front of a return with the pump running, never into the skimmer, and never add water to acid. Add at most about three quarters of the dose, circulate for 30 minutes, retest and add the rest.
Muriatic acid factors (26 fl oz for 7.8 → 7.4 at TA 100, 25.6 fl oz per 10 ppm TA, per 10,000 gal at 31.45 %): Trouble Free Pool, Pool School "Pool Math" and product labels. Read October 18, 2026.
Frequently asked questions
How much muriatic acid do I add to my pool?
For pH: about 26 fl oz of 31.45 % acid per 10,000 gallons lowers pH from 7.8 to 7.4 at TA 100. For alkalinity: about 25.6 fl oz per 10,000 gallons lowers TA by 10 ppm. Enter your readings above for the exact dose.
How quickly does muriatic acid lower alkalinity?
The drop shows within an hour once the acid has mixed. Bringing TA down a long way takes several rounds over a few days: acid takes pH to about 7.2, aeration lifts pH back while TA stays lower, then the next dose. Retest TA before each round.
Can you pour muriatic acid straight into a pool?
Yes, that is the usual way: pour it slowly into the deep end in front of a return with the pump running, close to the surface. Never pour it into the skimmer and never add water to acid. Pre-diluting it in a bucket of pool water, acid into water, works too.
How do I lower total alkalinity in my pool?
With acid and aeration. Add muriatic acid to bring pH to about 7.2, which lowers TA too, then aerate with jets pointed up or a waterfall until pH climbs back to 7.5. Repeat until TA is in range; each 10 ppm takes about 25.6 fl oz per 10,000 gallons.
Is muriatic acid the same as hydrochloric acid?
Yes. Muriatic acid is hydrochloric acid sold for pools and masonry, usually at 31.45 % (20° Baumé). Some jugs are weaker; enter the strength printed on your label above and the dose scales with it, since weaker acid needs more fluid ounces.