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Muriatic Acid Pool Calculator
Lowering pH or alkalinity? Get the amount of 31.45% muriatic acid for your gallons.
1 of 3: your gallons
Your dose appears here after the last question.
- 31.45%
- strength the doses assume
- Half
- the amount if your jug says 14.5%: double it
- Gloves + glasses
- every time
If your pH or alkalinity has crept too high, this muriatic acid pool calculator helps you work out how much acid to add. Enter your pool's gallons once and the site remembers them for every calculator. For a sense of scale: a pool holding 10,000 gallons, with alkalinity in the normal range and pH at 7.8, takes roughly 9 fl oz of the 31.45% acid to get down to 7.5. All doses here assume 31.45% muriatic acid. | Goal | Dose per 10,000 gallons | |---|---| | Lower pH from 7.8 to 7.5 | 9 fl oz | | Lower alkalinity by 10 ppm | 26 fl oz | ppm (parts per million) is the number your test strip or kit shows. Where you want pH: 7.4 to 7.6 (7.2 through 7.8 still works).
How many gallons does your pool hold?
Each dose starts with how much water you're treating, and the figures here use US gallons. For a rectangle, take the surface area in square feet, multiply by the average depth in feet, then multiply by 7.48. If your pool is round or oval, swap in 5.9 instead of 7.48.
Does the floor slope? Then your average depth is simply the midpoint of the shallow and deep ends. Here are three common sizes, all assuming the water averages 4.5 feet deep: a 12 x 24 ft pool holds roughly 9,690 gallons, a 16 x 32 ft pool about 17,200, and a 20 x 40 ft pool around 26,900.
How much muriatic acid should you add to your pool?
Three things set the dose: your gallons, how far down the pH needs to go, and your total alkalinity. Total alkalinity describes how much your water pushes back against pH changes. The higher it is, the more acid it takes to move pH the same distance.
The 9 fl oz dose lowers pH from 7.8 to 7.5 in 10,000 gallons at normal alkalinity, and the separate 26 fl oz dose lowers alkalinity by 10 ppm. If your pH reads 7.8, plan on 9 fl oz for 10,000 gallons or 18 fl oz for 20,000. If your pH reads higher than 7.8, or your alkalinity isn't in the normal range, enter your readings in the calculator rather than guessing from these numbers.
For the same starting readings, use half the listed dose for 5,000 gallons or twice the dose for 20,000 gallons.
Lowering alkalinity with acid
Taking total alkalinity down calls for much more acid than a small pH fix does. For each 10 ppm you want out of 10,000 gallons, plan on roughly 26 fl oz of the 31.45% acid.
Total alkalinity should sit at 80 to 120 ppm. In a 20,000-gallon pool, each 10 ppm you lower takes double the 10,000-gallon amount.
What strength is your jug?
Check the percentage on your jug's label. Every dose here is for 31.45% acid, so a different strength would need a different amount.
Adding the acid safely
Muriatic acid is powerful stuff, and a few simple habits protect both you and your pool.
- 1. Get the pump running first, so the acid circulates rather than collecting in one place.
- 2. Measure out your dose, and if you're diluting, pour the acid into the water. Never pour water into acid.
- 3. Pour in front of a return jet, where moving water carries it away fast.
- 4. One chemical at a time, and never let acid meet chlorine.
- 5. Give the acid about 30 minutes to mix, then test the pH again.