How to lower your pool’s pH
Updated:
High pH stings eyes, reduces chlorine efficiency, and can cloud water. Lower it with muriatic acid (or dry acid). The amount depends on how far you’re dropping pH and your alkalinity. Use the calculator for the exact dose.
Why high pH matters
The CDC explains that chlorine kills germs less effectively as pH rises, especially above 8.0, which is why it recommends keeping pH between 7.0 and 7.8. The MAHC Annex adds that high pH pushes water toward calcium scale.
pH targets
| Target | Range | Source |
|---|---|---|
| Required range | 7.0–7.8 | CDC; MAHC 5.7.3.4.1 |
| Hayward and Pentair manuals | 7.2–7.8 | The range the app uses for pools |
| When balancing water | 7.2–7.6 | MAHC Annex 5.7.4.6 |
| Calculator default | 7.5 | Inside all three ranges |
How alkalinity changes the dose
Amounts from the same engine the calculator runs, with no CYA.
| Change | Alkalinity | 31.45% muriatic acid, 10,000 gal |
|---|---|---|
| pH 7.8 to 7.6 | TA 100 | 5 fl oz |
| pH 8.0 to 7.5 | TA 70 | 9 fl oz |
| pH 8.0 to 7.5 | TA 100 | 12 fl oz |
| pH 8.0 to 7.5 | TA 150 | 19 fl oz |
Step by step
- Test pH and alkalinityAlkalinity is the buffer, so it sets how much acid you need: at TA 150 you need about twice the acid of TA 70 for the same drop. If you use stabilizer, test CYA too. It registers as alkalinity, and the calculator subtracts its share.
- Work out the doseEnter pH, alkalinity and CYA in the calculator. As a guide, taking 10,000 gallons from 8.0 to 7.5 at TA 100 takes about 12 fl oz of 31.45% muriatic acid.
- Add acid to the deep endPour slowly into the deep end with the pump running. Always add acid to water, never water to acid, and wear gloves and eye protection, as Hayward and Pentair both specify when handling muriatic acid.
- Aerate if alkalinity is fineAcid lowers alkalinity too. If TA is already good, aerate (jets/fountains) afterward to bring pH back up while TA stays down.
- Re-test before adding moreLet the pump mix the acid through the whole pool, then re-test before adding more, since a second dose based on an early reading can overshoot.
FAQ
Why does my pH keep rising?
Usually high alkalinity or aeration, common in salt pools and spas. The MAHC Annex describes alkalinity as a source of rising pH as carbon dioxide leaves the water. Bringing alkalinity toward 60–90 ppm, the range Trouble Free Pool uses for liquid chlorine and salt pools, steadies pH.
Muriatic acid or dry acid?
Both lower pH. Dry acid (sodium bisulfate) is easier to handle and gives off less fume, but it adds sulfate every time you use it. Muriatic acid adds only chloride.
Sources
- CDC, Home Pool and Hot Tub Water Treatment and Testing (May 10, 2024). The 7.0–7.8 range and chlorine weakening as pH rises
- CDC, Model Aquatic Health Code, 5th edition (2024), Code Language. Sections 5.7.3.4.1 (pH) and 5.7.4.4.1 (alkalinity)
- CDC, Model Aquatic Health Code, 5th edition (2024), Annex. Sections 5.7.3.4 (high pH and scale), 5.7.4.4.1 (pH rise from carbon dioxide) and 5.7.4.6 (pH 7.2–7.6)
- Trouble Free Pool, Pool Chemical Levels: Pool Industry vs TFP (December 21, 2025). Alkalinity of 60–90 ppm for a steadier pH
- Hayward, AquaRite 900 Series Electronic Chlorine Generator manual (092623 Rev D). Acid handling: add acid to water, gloves and eye protection
- Pentair, IntelliChlor IC15/IC20/IC40/IC60 Installation and User’s Guide (P/N 520589 Rev. R, 2023). Acid handling: add acid to water, gloves and eye protection
Related
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