Pool pH & alkalinity calculator
Not sure? Use the pool volume calculator.
Adjust pH
Most commercial pools target 7.4–7.6.
Enter 0 for unstabilized indoor pools.
Adjust total alkalinity
Common range 60–120 ppm; follow your code.
Estimates for typical pool water. Always follow the product label, your state/local code and your certified pool operator. Add about three-quarters of a pH or alkalinity dose first, circulate, and re-test before adding the rest. Never mix chemicals or add acid and chlorine at the same time.
Quick answer
How much acid lowers pH depends on total alkalinity. In 10,000 gallons with 100 ppm alkalinity, about 10.7 fl oz of 31.45% muriatic acid lowers pH from 7.8 to 7.4; at 60 ppm it takes about 6.5 fl oz. To lower alkalinity 10 ppm takes about 25.6 fl oz of acid, and to raise it 10 ppm, 1.4 lb of baking soda.
- Higher alkalinity = more acid per 0.1 pH.
- Acid lowers pH and alkalinity; aeration raises pH without raising alkalinity.
- CO₂ lowers pH without lowering alkalinity.
- MAHC pH range: 7.0–7.8; close below 6.5 or above 8.0.
Muriatic acid to lower pH 7.8 → 7.4 (per 10,000 gal, no CYA)
| Total alkalinity | Muriatic acid 31.45% | Dry acid (93%) | CO₂ |
|---|---|---|---|
| 60 ppm | 6.5 fl oz | 8.7 oz | 3.2 oz |
| 80 ppm | 8.6 fl oz | 11.6 oz | 4.2 oz |
| 100 ppm | 10.7 fl oz | 14.5 oz | 5.3 oz |
| 120 ppm | 12.9 fl oz | 1.1 lb | 6.3 oz |
| 150 ppm | 16.1 fl oz | 1.4 lb | 7.9 oz |
| To change alkalinity | Product | Per 10 ppm per 10,000 gal |
|---|---|---|
| Raise | Sodium bicarbonate (baking soda) | 1.4 lb |
| Lower | Muriatic acid 31.45% | 25.6 fl oz |
| Lower | Dry acid (sodium bisulfate 93%) | 2.2 lb |
How the pH math works
Pool water is buffered mainly by carbonate alkalinity (bicarbonate and carbonate) plus cyanuric acid if the pool is stabilized. The calculator first subtracts the CYA contribution from your total alkalinity reading (roughly CYA ÷ 3 at pH 7.5), then calculates how much acid or soda ash shifts the carbonate balance to your target pH. This is why one fixed rule like "1 quart per 0.2 pH" is wrong for most commercial pools.
- Muriatic acid — cheapest per dose; add slowly in front of a return or into the surge tank with the pump running.
- Dry acid — easier to handle, but adds sulfate and raises TDS.
- CO₂ feed — popular on commercial controllers because it lowers pH without dragging alkalinity down.
- Soda ash — raises pH and alkalinity; add slowly to avoid clouding. Aeration raises pH without chemicals.
How to lower pool pH with muriatic acid
- Test pH, alkalinity and CYA. You need all three to calculate the acid dose accurately.
- Calculate the dose. Enter your volume, readings and target pH in the calculator.
- Add three-quarters of the dose. With the pump running, pour the acid slowly in front of a return or into the surge tank.
- Circulate and re-test. Wait at least one turnover, re-test, and add the rest if needed.
- Log it. Record the product, amount, time and re-test result in the pool log.
Frequently asked questions
How much muriatic acid do I add to lower pH?
In 10,000 gallons with 100 ppm alkalinity, about 10.7 fl oz of 31.45% muriatic acid lowers pH from 7.8 to 7.4. A 100,000-gallon pool at 90 ppm alkalinity needs roughly 66 fl oz (about half a gallon) to go from 7.8 to 7.5.
Should I lower alkalinity or pH first?
Adjust alkalinity first, because it controls how much pH moves. If both are high, add acid to lower alkalinity, then aerate to bring pH back up.
What raises pH without raising alkalinity?
Aeration: fountains, return jets aimed at the surface, waterfalls or air blowers drive off CO₂ and raise pH while alkalinity stays the same.
What is the right pH for a commercial pool?
The MAHC allows 7.0–7.8 and many states require 7.2–7.8. Most operators target 7.4–7.6 for bather comfort and chlorine effectiveness.
How long should I wait to re-test after adding acid?
Wait at least one turnover — about 6 hours in a typical commercial pool, less with good circulation near the addition point — before re-testing for a final reading.
This page is an educational summary, not legal advice. Pool and spa codes differ by state and county and change over time — always confirm requirements with the health department that inspects your facility.