Muriatic Acid Pool Calculator
High pH weakens chlorine and causes scale. Enter your pool size and readings to see how much acid to add, in fluid ounces.
Updated November 2026
How Much Muriatic Acid Lowers Pool pH?
About 12 fluid ounces of full strength (31.45%) muriatic acid per 10,000 gallons lowers pH by roughly 0.2. To lower total alkalinity, about 26 fluid ounces per 10,000 gallons removes 10 ppm.
How far pH moves depends on your alkalinity. If you are unsure, add half the dose, circulate for 30 minutes and retest. Using dry acid? About 1.3 ounces by weight does the work of 1 fluid ounce of muriatic acid.
Muriatic Acid Chart: Lowering pH
Full strength (31.45%) muriatic acid needed by pool size and how far you are lowering pH:
| Lower pH by | 10k gal | 15k gal | 20k gal | 25k gal | 30k gal |
|---|---|---|---|---|---|
| 0.2 | 12 fl oz | 18 fl oz | 24 fl oz | 30 fl oz | 36 fl oz (1.1 qt) |
| 0.4 | 24 fl oz | 36 fl oz (1.1 qt) | 48 fl oz (1.5 qt) | 60 fl oz (1.9 qt) | 72 fl oz (2.2 qt) |
| 0.6 | 36 fl oz (1.1 qt) | 54 fl oz (1.7 qt) | 72 fl oz (2.2 qt) | 90 fl oz (2.8 qt) | 108 fl oz (3.4 qt) |
| 0.8 | 48 fl oz (1.5 qt) | 72 fl oz (2.2 qt) | 96 fl oz (3 qt) | 120 fl oz (3.8 qt) | 1.1 gal |
Based on 12 fl oz per 10,000 gallons for each 0.2 of pH. Water with high alkalinity needs more. Split anything over 0.4 into two doses.
Muriatic Acid Chart: Lowering Alkalinity
Full strength (31.45%) muriatic acid needed by pool size and how far you are lowering total alkalinity:
| Lower alkalinity by | 10k gal | 15k gal | 20k gal | 25k gal | 30k gal |
|---|---|---|---|---|---|
| 10 ppm | 25.5 fl oz | 38 fl oz (1.2 qt) | 51 fl oz (1.6 qt) | 64 fl oz (2 qt) | 77 fl oz (2.4 qt) |
| 20 ppm | 51 fl oz (1.6 qt) | 77 fl oz (2.4 qt) | 102 fl oz (3.2 qt) | 1 gal | 1.2 gal |
| 30 ppm | 77 fl oz (2.4 qt) | 115 fl oz (3.6 qt) | 1.2 gal | 1.5 gal | 1.8 gal |
| 40 ppm | 102 fl oz (3.2 qt) | 1.2 gal | 1.6 gal | 2 gal | 2.4 gal |
This is the total over several days, not one dose. Add enough to bring pH to about 7.0 to 7.2, aerate until pH is back near 7.6, and repeat.
How do I add muriatic acid safely?
- Run the pump and keep swimmers out.
- Measure the dose of muriatic acid into a clean plastic measuring cup used only for pool acid.
- Pour slowly into the deep end, close to the water surface, away from the skimmer and any metal fittings. In a vinyl or fiberglass pool, dilute it first.
- To dilute: fill a plastic bucket with pool water, then add the acid to the water. Never add water to acid.
- Wait 30 minutes with the pump running, then retest pH.
Add acid and chlorine at least 30 minutes apart, and never in the same spot at the same time. See what order to add pool chemicals.
How do I lower alkalinity without wrecking pH?
Acid lowers pH and alkalinity together. To bring alkalinity down and keep pH in range, work in rounds:
- Add enough acid to bring pH to about 7.0 to 7.2. Do not go lower.
- Aerate. Point the return jets up, or run a fountain or spa jets. This raises pH without raising alkalinity.
- When pH is back near 7.6 to 7.8, test alkalinity and repeat until it reads 80 to 120 ppm.
Expect it to take several days. Only chase alkalinity if it is causing trouble. See does high alkalinity cause cloudy pool water.
Muriatic acid or dry acid?
| Muriatic acid | Dry acid | |
|---|---|---|
| Chemical | Hydrochloric acid, 31.45% | Sodium bisulfate |
| Form | Liquid | Granules |
| To match 1 fl oz of muriatic acid | 1 fl oz | About 1.3 oz by weight |
| Handling | Fumes, splashes | Easier to measure and store |
| Adds to the water | Chloride | Sulfate, which builds up over time |
| Cost per dose | Lower | Higher |
Half-strength muriatic acid, about 14 to 16% hydrochloric acid, needs a little more than twice the amount. Low-fume products vary in strength, so read the percent on the label before you measure.
Frequently Asked Questions
How much muriatic acid does it take to lower pH 0.2?
About 12 fluid ounces of 31.45% acid per 10,000 gallons. A 20,000 gallon pool needs about 24 fluid ounces, or 3 cups.
How much muriatic acid lowers alkalinity 10 ppm?
About 26 fluid ounces of 31.45% acid per 10,000 gallons. Add it over several rounds with aeration in between so pH does not fall below 7.0.
How long after adding muriatic acid can I swim?
About 30 to 60 minutes with the pump running, once pH tests between 7.2 and 7.8.
Can I add muriatic acid and chlorine at the same time?
No. Mixed together they release chlorine gas. Add one, wait at least 30 minutes with the pump running, then add the other in a different spot.
Why does my pH keep going up?
The usual causes are high total alkalinity, a salt water chlorine generator, new plaster, and water features that stir in air. Lowering alkalinity toward 80 ppm slows the rise.
Sources
- CDC: Pool chemical injuries and how to prevent them (MMWR, 2019)
- HASA: muriatic acid product information
Next: balance the rest
Once pH is in range, check alkalinity, chlorine and stabilizer.
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