Free pool tool
Muriatic Acid Calculator
Choose whether you are lowering pH or total alkalinity, enter your readings, and the calculator works out how much muriatic acid or dry acid to add. The pH dose is adjusted for your alkalinity, because that is what decides how far each ounce moves the reading.
Not sure? Work out your pool volume.
Higher alkalinity needs more acid.
Add Muriatic acid (31.45%)
20 fl oz
- This also lowers total alkalinity by about 5 ppm.
- pH dosing is the least precise of the pool chemicals because borates, stabilizer and fresh plaster all buffer it. Add the acid in two halves and re-test between them.
- Pour it slowly into the deep end in front of a return with the pump running. Always add acid to water, never water to acid.
- Add about three quarters of the dose, let the pump circulate for an hour, and re-test before adding the rest. Never mix chemicals together, and always add chemicals to water rather than water to chemicals.
How it works
Lowering pH and Lowering Alkalinity Are Different Jobs
Total alkalinity is the water's buffer. It soaks up acid and holds pH steady, which is useful most of the time and is also why the same amount of acid moves pH much further in a low-alkalinity pool than in a high one, so the calculator scales the pH dose with alkalinity.
Lower TA: 25.6 fl oz of 31.45% acid per 10 ppm per 10,000 gal
The alkalinity rate isn't an estimate. Each molecule of hydrochloric acid neutralizes a fixed amount of alkalinity, and 25.6 fl oz of 31.45% acid carries just enough to remove 10 ppm from 10,000 gallons. pH is less predictable, because borates, cyanuric acid and fresh plaster all buffer it to some degree, so treat a pH dose as a starting point and re-test.
Worked examples
A 15,000-Gallon Pool
Lowering pH from 7.8 to 7.5 at 100 ppm alkalinity. The change is 0.3, or one and a half steps of 0.2. That is 6.5 × 1.5 × 1.5 for the pool size, which comes to about 15 fl oz of 31.45% muriatic acid. It also lowers alkalinity by about 4 ppm. At 150 ppm alkalinity the same pH change takes about 22 fl oz, and at 60 ppm about 8.8 fl oz.
Lowering total alkalinity from 150 to 100 ppm. That is five steps of 10 ppm, so 25.6 × 5 × 1.5 gives 192 fl oz, or 1.5 gallons of 31.45% acid. With half-strength acid it would be about 3.53 gallons, and with dry acid about 15.8 lb.
Lowering alkalinity
Acid Down, Then Air Up
Acid lowers pH and alkalinity together, so there is no way to lower alkalinity with acid alone and leave pH where it was. The method that works is to add the acid, accept that pH drops, and then aerate the water. Point the returns upward, run a waterfall or fountain, or add an air feature. Aeration drives off carbon dioxide, which raises pH without adding alkalinity back.
Repeat the cycle until alkalinity reaches its target, keeping pH above 7.0 so plaster and metal aren't exposed to aggressive water. For a large drop, spread the work over several days. The guide to lowering pool pH covers the testing side in more detail, and the LSI calculator shows whether the finished water is balanced.
Safety
Handling Muriatic Acid
Muriatic acid is concentrated hydrochloric acid, and its fumes corrode metal and irritate lungs and eyes. Wear chemical-resistant gloves and eye protection, and keep your face away from the open jug. Pour it slowly into the deep end in front of a return with the pump running, so it disperses before it reaches a surface.
Always add acid to water, never water to acid. Never mix it with chlorine, because the two release chlorine gas, and store the jugs apart from chlorine products. Add about three quarters of the calculated dose, let the pump circulate for an hour, and re-test before adding the rest.
For pool service companies
The same maths runs at every stop in Pool Runs
These calculators use the dosing and saturation-index formulas built into the Pool Runs technician app. A tech logs the readings at the pool, the app works out the doses for that pool's own volume, and the visit lands in the customer's service history and report without anyone typing it up later.
- Readings and doses saved against each pool, with the saturation index for every visit
- A mobile app that works offline in a backyard with no signal
- Chemicals and parts tracked on every truck and in the shop
Try Pool Runs free
Free for 30 days, month to month, with white-glove onboarding to move your customers in.
Questions
Muriatic Acid Calculator FAQ
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