Lowering pH with muriatic acid
fl oz of 31.45 % muriatic acid = (pH now − target) ÷ 0.4 × 26 × gallons ÷ 10,000 × TA ÷ 100
About 26 fl oz of 31.45 % muriatic acid takes 10,000 gallons from pH 7.8 to 7.4 at a total alkalinity of 100 ppm. A 20,000-gallon pool from 7.8 to 7.6 at TA 120 needs 31.2 fl oz. Pour the acid slowly in front of a return with the pump running, never into the skimmer, and wear gloves and eye protection. The muriatic acid calculator also gives the dose to lower alkalinity.
Raising pH with soda ash
oz of soda ash = (target − pH now) ÷ 0.2 × 6 × gallons ÷ 10,000 × TA ÷ 100
About 6 oz of soda ash (sodium carbonate) raises 10,000 gallons by 0.2 pH at TA 100. Soda ash raises alkalinity a little too. If your pH is fine but alkalinity is low, use baking soda instead: the pool alkalinity calculator works it out. Once pH is in range, check your chlorine with the pool chlorine calculator.
Both doses are estimates: pH does not move in a straight line, and borates or a high stabilizer level change the response. Add about three quarters of the dose, circulate, retest and add the rest.
Muriatic acid (26 fl oz for 7.8 → 7.4 per 10,000 gal at TA 100) and soda ash (6 oz per 0.2 pH) factors: Trouble Free Pool, Pool School "Pool Math" and product labels. Read October 18, 2026.
Frequently asked questions
Will shocking a pool lower the pH?
Usually not. Cal-hypo and liquid chlorine are alkaline and push pH up a little when you add them; dichlor is close to neutral; trichlor tablets are acidic and pull pH down over time. Test pH an hour after shocking and correct it here if it left 7.4 to 7.6.
Is 8.2 pH too high for a pool?
Yes. Above about 7.8 chlorine works more slowly, scale forms on surfaces and in the heater, and the water can turn cloudy. Bring it to 7.4 to 7.6 with muriatic acid: in 15,000 gallons at TA 100, going from 8.2 to 7.6 takes about 58 fl oz.
Will baking soda raise pH in a pool?
A little. Baking soda mainly raises total alkalinity; its own pH is about 8.3, so it nudges pool pH up only slightly. To raise pH without much change in alkalinity, use soda ash: about 6 oz lifts 10,000 gallons by 0.2 at TA 100.
How much muriatic acid lowers the pH of a 20,000 gallon pool?
About 52 fl oz of 31.45 % muriatic acid takes 20,000 gallons from pH 7.8 to 7.4 at a total alkalinity of 100 ppm, and 65 fl oz from 8.0 to 7.5. Higher alkalinity needs proportionally more. Add three quarters, circulate for 30 minutes, retest.
What is the right pH for a swimming pool?
7.2 to 7.8 is the accepted range, and 7.4 to 7.6 the usual aim: comfortable for eyes, good for chlorine and gentle on plaster and metal. Below 7.2 the water turns corrosive; above 7.8 chlorine slows down and scale forms.