How Much Muriatic Acid to Add to Your Pool — Calculator
Calculate how much muriatic acid to add to lower your pool's pH or total alkalinity.
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Safety first — muriatic acid is corrosive
Always pre-dilute in a bucket of pool water before adding. Pour acid into water, never water into acid. Wear eye protection and gloves. Add near a return jet with the pump running, never near the skimmer. Never mix with chlorine or other chemicals.
Lower pH vs lower total alkalinity — what's the difference?
Both use the same chemical (muriatic acid), but the goal determines how much you add and what you do next.
Lowering pH is the most common use. If your pH is above 7.8, acid brings it back into the 7.4–7.6 target range. Adding acid also drops TA slightly, which is usually fine unless your TA is already low.
Lowering total alkalinity uses a larger acid dose to deliberately reduce TA. Because this also drops pH sharply, you then aerate the water to drive CO₂ off and raise pH back to 7.4–7.6 — without raising TA. This is the correct sequence when TA is high and causing persistent pH drift upward.
Fix TA before chasing pH
If your pH keeps drifting up no matter how much acid you add, high total alkalinity is almost always the cause. Bring TA to 60–80 ppm first — then pH stabilizes and requires far less maintenance acid over the season.
How the muriatic acid dose is calculated
For pH: The acid dose is proportional to the pH drop and the current alkalinity. Higher TA means more buffering capacity, so more acid is required for the same pH change.
For TA: The relationship is direct — each ppm of TA reduction in a given volume requires a fixed amount of acid.
Worked example: lowering pH
A 15,000-gallon pool tests at pH 7.9 with TA 100 ppm. Target is pH 7.4 — a drop of 0.5 pH units.
Dose = 0.5 × 100 × 0.534 × (15,000 ÷ 10,000) = ~40 fl oz (1.25 quarts) of 31.45% acid. Split into two doses of ~20 fl oz each. Add the first dose near a return jet, circulate for 1 hour, retest — then add the second if pH is still above target. Never add more than 1 quart at a time to avoid overshooting.
Worked example: lowering total alkalinity
A 10,000-gallon pool tests at TA 120 ppm. Target is TA 80 ppm — a reduction of 40 ppm.
Dose = 40 × (10,000 ÷ 10,000) × 2.6 = ~104 fl oz (3.25 quarts) of 31.45% acid. Split into 3–4 doses of ~1 quart each. Add each dose near a return jet, circulate for 1 hour, retest TA before continuing. Once TA reaches 80 ppm, aerate — run a waterfall, jets, or air bubbler for several hours to drive off CO₂ and bring pH back to 7.4–7.6. Do not add soda ash or baking soda to recover pH after a TA reduction — that undoes the TA correction.
Frequently asked questions
How much muriatic acid lowers pH by 0.2?
For a 10,000-gallon pool at TA 100 ppm: about 11 fl oz of 31.45% acid. For a 15,000-gallon pool: about 16 fl oz. The exact amount varies with your total alkalinity — higher TA means more buffering, so more acid is needed for the same pH drop. Use the calculator above for your specific numbers.
How much muriatic acid lowers total alkalinity by 10 ppm?
For a 10,000-gallon pool: about 26 fl oz (just under 1 quart) of 31.45% muriatic acid lowers TA by 10 ppm. For a 15,000-gallon pool: about 39 fl oz. Add in stages of 1 quart or less, circulate for 1 hour, and retest before continuing. After TA is in range, aerate the water — waterfall, jets, or air bubbler — to raise pH back to 7.4–7.6 without raising TA again.
How long after adding muriatic acid can I swim?
Wait at least 30 minutes with the pump running, then retest pH before swimming. If pH is in the 7.4–7.6 range, it's safe. Never enter the pool immediately after adding acid — the localized concentration near the addition point is far higher than the overall pool reading, even with the pump on.
Should I lower pH or total alkalinity first?
If TA is above 120 ppm, fix TA first. High TA is the root cause of pH that drifts upward no matter how much acid you add. Use the "Lower Alkalinity" mode, bring TA to 60–80 ppm, then aerate to recover pH. Once TA is in range, pH becomes stable and needs far less maintenance acid.
What happens if I add too much acid?
pH crashes below 7.0, making the water corrosive — it etches plaster, damages metal fittings, and irritates swimmers. If this happens, add soda ash (sodium carbonate) to bring pH back to 7.4–7.6. To prevent it: split large doses, add no more than 1 quart at a time, and retest after each dose before continuing.
Is dry acid (sodium bisulfate) a substitute for muriatic acid?
Yes — it does the same job and is safer to handle, with no fumes. The trade-off: it adds sulfates to your water, which accumulate over time and can damage plaster and pool heaters, especially in saltwater pools. For most residential pools, muriatic acid is the better long-term choice. Dry acid works well for spas or when liquid acid storage isn't practical.