How much muriatic acid for a 5,000 gallon pool

In a 5,000 gallon pool with alkalinity 80, about 4.1 fl oz (123 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, 13 fl oz (379 mL) lowers TA by 10 ppm.

Muriatic acid doses for 5,000 gallons

pH rows assume TA 80, CYA 40 and 77 °F water. Your dose changes with TA: higher TA needs more.
Change	31.45% acid	14.5% acid
pH 7.8 → 7.5	4.1 fl oz	9.7 fl oz
pH 8.0 → 7.5	5.9 fl oz	14 fl oz
pH 8.2 → 7.6	5.7 fl oz	13 fl oz
pH 7.7 → 7.4	5 fl oz	12 fl oz

Then aerate to bring pH back up. See the alkalinity guide.
Lower alkalinity	31.45% acid	14.5% acid
TA −10 ppm	13 fl oz	30 fl oz
TA −20 ppm	26 fl oz (2 parts)	0.47 gal
TA −30 ppm	0.3 gal (3 parts)	0.7 gal

Run it with your numbers

Add

4.1fl oz

of Muriatic acid 31.45%

122 mL½ cup

Lowers pH from 7.8 to 7.5 in 5,000 gal at TA 80. TA afterwards: about 77 ppm.

Side effects: TA −3.2 ppm.
Never add acid and chlorine together or in the same spot: mixing them releases toxic chlorine gas. Let the first one circulate before adding the other (the wait is shown on each step).
Pour it slowly in front of a return jet with the pump running.
Retest after the water has circulated.

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.

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About muriatic acid

Wear 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 16 fl oz 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.

Dosing a 5,000 gallon pool

That is about the size of a 15 ft round × 52 in above-ground pool (about 5,070 gal), or a 16 ft round × 48 in above-ground pool (about 5,260 gal). At 5,000 gallons, most doses are measured in fluid ounces or ounces rather than gallons or pounds. Above-ground pools of this size usually have vinyl liners, so keep calcium hardness modest and add everything in front of a return jet, away from the liner wall.

Questions

How much muriatic acid do I add to a 5,000 gallon pool?

To lower pH from 7.8 to 7.5 at TA 80, about 4.1 fl oz of 31.45% acid. To lower alkalinity by 10 ppm, 13 fl oz.

How long after adding muriatic acid can I swim?

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.

Is 14.5% acid weaker?

Yes. It is the same acid at about half the strength, so you need roughly twice as much: 30 fl oz lowers TA 10 ppm in 5,000 gallons.