pH Calculator
Calculate how much muriatic acid or soda ash to add to raise or lower your pool pH to the ideal 7.2-7.6 range.
Safety
Never add acid and base at the same time. Add chemicals with the pump running and distribute evenly. Wait at least 30 minutes between additions and retest. Muriatic acid produces fumes — add outdoors, downwind.
Per 10,000 gallons at TA near 100 ppm, moving pH by 0.1 takes about 6.4 fl oz of muriatic acid to lower it, or 6 oz of soda ash to raise it. Aim for 7.2–7.6. The amount scales with your alkalinity, so a high-TA pool needs more — dose in thirds and retest. Enter your pool's numbers above for the exact amount.
The Dose Depends On Alkalinity, Not Just pH
Two pools both read pH 7.8 and both want 7.4. One takes half a cup of acid, the other takes three times that. The difference is total alkalinity — the buffer that has to be pushed through before pH will move at all. That is what "acid demand" means, and it is why a dose that worked on your neighbour's pool overshoots or does nothing in yours.
The figures on this page assume TA near 100 ppm, the middle of the normal range. At 150 ppm expect to need meaningfully more; at 60 ppm, less, and pH will move faster and further than you intended. Target band is 7.2–7.6, and 7.4–7.5 is where most pools are happiest.
pH Dose Chart
Per 10,000 gallons at TA ≈ 100 ppm. Double it for 20,000 gallons. Add in thirds and retest rather than dosing the full amount in one go.
| pH change | Muriatic acid to lower |
Dry acid to lower |
Soda ash to raise |
Borax to raise |
|---|---|---|---|---|
| 0.1 | 6.4 fl oz | 5.3 oz | 6.0 oz | 20.0 oz |
| 0.2 | 12.8 fl oz | 10.6 oz | 12.0 oz | 40.0 oz |
| 0.3 | 19.2 fl oz | 15.9 oz | 18.0 oz | 60.0 oz |
| 0.4 | 25.6 fl oz | 21.2 oz | 24.0 oz | 80.0 oz |
| 0.5 | 32.0 fl oz | 26.5 oz | 30.0 oz | 100.0 oz |
| 0.6 | 38.4 fl oz | 31.8 oz | 36.0 oz | 120.0 oz |
Muriatic acid at 31.45%, dry acid as sodium bisulfate, borax as 20 Mule Team. Enter your real volume and readings above for a dose matched to your pool.
Muriatic acid or dry acid
Muriatic acid is hydrochloric acid, cheap, fast, and leaves nothing behind but chloride. It also fumes, corrodes anything metal stored near it, and burns skin instantly. Buy the low-fume 14.5% version if the full-strength jug makes you nervous — it is the same chemical at half concentration, so double the dose.
Dry acid (sodium bisulfate) is a granular powder that is far easier to carry, store and measure, which is why it dominates in cold climates and small pools. The cost is sulfate: every dose leaves it behind permanently, and heavy long-term use builds levels that attack plaster and shorten salt cell life. Occasional use is fine; as the year-round default in a pool you dose weekly, muriatic is the better habit.
Either one goes in with the pump running, poured slowly across the deep end away from fittings and the liner, never through the skimmer, and never within hours of a chlorine dose. Wait 30 minutes before retesting — the reading before that is not the pool, it is the plume.
Raising pH without raising alkalinity
Soda ash (sodium carbonate) raises pH quickly and pulls TA up with it, which is ideal when both are low and wrong when TA is already fine. Borax moves pH with almost no TA effect, at roughly three times the weight. And if TA is where you want it, the cheapest option is no chemical at all: aerate. Point a return jet at the surface, run the spa spillover or the waterfall, and pH climbs on its own as dissolved carbon dioxide leaves the water. If you keep mixing the two up, baking soda vs soda ash spells out which one raises TA and which raises pH.
Why it keeps climbing back
Upward drift is the pool's natural state, not a fault. Water at typical alkalinity holds more dissolved CO2 than it wants to, and anything that agitates the surface — waterfalls, spillovers, aerated jets, a salt cell producing gas at the plates — releases it and pushes pH up. Fresh plaster leaches alkaline material for its first season. Liquid chlorine and cal-hypo both nudge pH up on every dose.
If you are adding acid more than about once a week, the fix is not more acid: it is lowering total alkalinity, which cuts the CO2 reservoir driving the climb. Work that with the alkalinity calculator first. Some owners then add borates at 30–50 ppm as a secondary buffer, which flattens the drift further.
The chlorine-efficiency claim, corrected
The familiar chart says roughly half your free chlorine is in its active form at pH 7.5 and only about a fifth at pH 8.0, so high pH means weak chlorine. That is true — in water with no cyanuric acid. Once CYA is present, and in an outdoor pool it always is, most free chlorine is bound in the CYA reserve and stabilizer, not pH, becomes the dominant control on killing power. Between pH 7.5 and 8.0 the practical difference in a stabilized pool is small.
Control pH anyway — for scale on the tile and the salt cell, for corrosion and etching at the low end, for swimmer comfort, and because high pH throws off the accuracy of the tests you are making every other decision from. Just do not expect a green pool to clear because you dropped pH by 0.2. That is a chlorine job — size it with the shock calculator, or run the full panel in the right order with the water balance calculator.