Pool pH Calculator
Estimate the muriatic acid to lower pH or the soda ash to raise it. Enter your pool volume, current and target pH, and current total alkalinity, and get an estimated dose to nudge pH back into range.
Calculator
Add roughly 32.1 fl oz of muriatic acid to lower pH from 7.8 to 7.5 (estimate — acid demand depends on TA of 100 ppm; add ~¾, re-test, then adjust).
pH sets how acidic or basic your water is on a 0-14 scale, and pool water is happiest around 7.4-7.6. Too high and chlorine loses bite, scale can form and the water clouds; too low and the water turns corrosive to plaster, metal and grout. You lower pH with an acid — almost always muriatic (hydrochloric) acid — and raise it with soda ash (sodium carbonate).
pH dosing is genuinely an estimate, because how far a given amount of acid moves pH depends on your total alkalinity, which acts as a buffer. That is why this tool asks for your current alkalinity and why you should always add part of the dose, re-test, and adjust.
Formula
To lower pH, the tool uses the standard field estimate for 31.45% muriatic acid at a typical alkalinity near 100 ppm:
muriatic acid (fl oz) ≈ (ΔpH ÷ 0.1) × 10.7 × (gallons ÷ 10,000)
To raise pH, it estimates soda ash:
soda ash (oz) ≈ (ΔpH ÷ 0.1) × 3.0 × (gallons ÷ 10,000)
where ΔpH is the absolute pH change. About 10.7 fl oz of muriatic acid lowers 10,000 gallons by roughly 0.1 pH at TA near 100; higher alkalinity resists the change, so treat the result as a starting point, not a precise number.
Worked example
A 10,000-gallon pool reads pH 7.8 and you want 7.5, with total alkalinity around 100 ppm:
- ΔpH = 7.8 − 7.5 = 0.3.
- muriatic acid ≈ (0.3 ÷ 0.1) × 10.7 × (10,000 ÷ 10,000) = 3 × 10.7 × 1 = ≈ 32 fl oz.
- Add about three-quarters (roughly 24 fl oz) first, circulate, re-test, then finish the adjustment.
To go the other way — say 7.2 up to 7.5 — the same ΔpH of 0.3 needs about 3 × 3.0 = 9 oz of soda ash for 10,000 gallons.
Raising and lowering pH in practice
Add muriatic acid slowly into the deep end with the pump running, and keep it well away from chlorine products — never mix them. Because pH and alkalinity move together, adjusting one shifts the other: bringing pH down with acid also lowers total alkalinity, so check both after dosing. Aerating the water raises pH without chemicals, which is handy when alkalinity is fine but pH is a touch low.
If your pH keeps drifting up, the cause is often high alkalinity acting as a pH “engine”; lowering TA usually settles pH. Keep total alkalinity in a sensible band first, then fine-tune pH. This tool sizes the nudge; your test kit and the product label set the target.
Fresh plaster and some fill waters push pH and alkalinity upward for weeks, so expect to add acid more often on a new or freshly refilled pool. Salt-chlorine generators also tend to nudge pH up over time. None of that changes the math here — it only changes how frequently you dose — which is exactly why the tool stores no schedule and simply sizes the next correction from your current reading.
Frequently asked questions
How much muriatic acid to lower pool pH?
As a field estimate, about 10.7 fl oz of muriatic acid lowers 10,000 gallons by roughly 0.1 pH when alkalinity is near 100 ppm. For a 0.3 drop in a 10,000-gallon pool that is around 32 fl oz. Add part of it, re-test, then adjust.
What pH should a pool be?
Aim for about 7.4-7.6. Below 7.2 the water becomes corrosive; above 7.8 chlorine weakens and scale can form. Follow your test kit and product label — this calculator sizes the dose, it does not set the ideal target.
Why is pH dosing only an estimate?
Total alkalinity buffers pH, so the same amount of acid moves pH more in low-alkalinity water and less in high-alkalinity water. Temperature and aeration matter too. That is why you should add about three-quarters of the dose, circulate, and re-test before adding more.
How do I raise pool pH?
Add soda ash (sodium carbonate) to raise pH; roughly 3 oz per 0.1 pH per 10,000 gallons as an estimate. Aerating the water — fountains, jets, returns pointed up — also raises pH gently without adding chemicals.
Does lowering pH also lower alkalinity?
Yes. Adding acid lowers both pH and total alkalinity, because the same acid neutralizes the buffer. Adjust alkalinity into range first, then fine-tune pH, and re-test both after any acid addition.