How much muriatic acid to lower pH in a 10,000 gallon pool?
To lower pH from 7.8 to 7.4 in a 10,000 gallon pool with 100 ppm alkalinity and 30 ppm stabilizer, you need about 13.7 fl oz (1.7 cups) of 31.45% muriatic acid. Add 10.2 fl oz (1.3 cups) first, run the pump, then retest.
How to work it out
- In short: alkalinity is the water’s buffer, so the more of it there is, the more acid it takes to move pH. The chemistry lines below work out how much.
- Carbonate alkalinity: 100 ppm TA minus the part of the test that is really stabilizer (30 ppm CYA) at pH 7.8
- Acid to move pH 7.8 → 7.4 with the CO₂ staying in the water: 5.3 ppm of alkalinity (as CaCO₃)
- 5.3 ppm × 37,854 L ÷ 50,044 mg per equivalent = 4.02 equivalents of acid
- 4.02 eq × 100 ml per equivalent (31.45% HCl) = 13.7 fl oz (1.7 cups)
Most pools drift up to about 7.8 between adjustments, and 7.4 is a comfortable target in the middle of the CDC’s 7.0–7.8 range. In a 10,000 gallon pool with normal alkalinity that takes well under a quart of acid.
Adjust for your project
More options: Temp · TDS
- Add this first, then retest
- 10.2 fl oz (1.3 cups)
- Alkalinity this also removes
- 5 ppm
- Acid per 10 ppm of alkalinity in this pool
- 25.7 fl oz (3.2 cups)
- Assumes 82°F water and 1,000 ppm dissolved solids — change them under More options.
- This is an estimate from carbonate chemistry. Borates, very high TDS, a pH test that is off by 0.1, or chlorine just added all change the real amount — which is why you add part, wait and retest.
10,000 gallons, pH 7.8 → 7.4, by total alkalinity
| Alkalinity | Acid to add (in total) | Alkalinity this also removes |
|---|---|---|
| 60 ppm | 9.1 fl oz (1.1 cups) | 4 ppm |
| 80 ppm | 11.4 fl oz (1.4 cups) | 4 ppm |
| 100 ppm | 13.7 fl oz (1.7 cups) | 5 ppm |
| 120 ppm | 15.9 fl oz (2 cups) | 6 ppm |
| 150 ppm | 19.4 fl oz (2.4 cups) | 8 ppm |
Why the dose depends on alkalinity
Alkalinity is the water’s buffer: the more of it there is, the more acid it takes to move pH. The same 7.8 to 7.4 change in this pool takes about 11.4 fl oz at 80 ppm TA and about 15.9 fl oz at 120 ppm. If you guess TA, you guess the dose.
- Add three-quarters first. About 10 fl oz, poured slowly into the deep end with the pump running. Retest after a few hours of circulation; finish with the rest only if pH is still above target.
- Label limit. One muriatic label says never more than 16 oz per 10,000 gallons at one time — this dose fits in one go.
- Dry acid instead? About 1.1 lb of 93.2% sodium bisulfate does the same job.
- Keep it apart from chlorine. Add acid and chlorine hours apart, in different spots, with separate measuring cups.
- Why does it come back? Aeration (waterfalls, spa spillovers) drives off carbon dioxide and pushes pH up again. If you’re adding acid every few days, lowering alkalinity a little slows the drift.
If alkalinity is the real problem, see how much muriatic acid to lower alkalinity in a 10,000 gallon pool. Hot tubs need much less: how much muriatic acid to lower pH in a hot tub.
Different size? Use the full Muriatic Acid Calculator (pH & Alkalinity Down).
What you’ll need
- Muriatic acid (31.45% HCl)Budget price
Lowers pH and alkalinity. Strong and fuming — use goggles and gloves, add it slowly to the deep end with the pump running, and store it away from chlorine.
See options on Amazon (opens in a new tab) - Chemical splash gogglesBudget price
Muriatic acid and liquid chlorine splash. Indirect-vent goggles cost little next to an eye injury.
See options on Amazon (opens in a new tab) - Measuring pitcher (marked in oz and ml)Budget price
Measure doses instead of glugging from the jug. Keep one for acid and a separate one for chlorine.
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Frequently asked questions
How much muriatic acid to lower pH from 8.0 to 7.5 in 10,000 gallons?
About 13.3 fl oz (1.7 cups) of 31.45% acid at 100 ppm alkalinity.
How much dry acid to lower pH from 7.8 to 7.4 in 10,000 gallons?
About 1.14 lb (18.3 oz) of 93.2% sodium bisulfate (dry acid).
How much muriatic acid to lower pH in a 20,000 gallon pool, 7.8 to 7.4?
About 27.3 fl oz (3.4 cups) of 31.45% acid with 100 ppm alkalinity — split it into two additions.
Other common sizes
Sources
- INEOS — Hydrochloric acid 20° Bé product sheet (opens in a new tab) — 20° Baumé hydrochloric acid is 31.45–32.56% HCl, specific gravity about 1.16.
- HASA / Orenda — Muriatic acid product page (opens in a new tab) — 31.45% hydrogen chloride; label limit of one quart per 20,000 gallons per 24 hours to reduce pH.
- HASA — Acid 15 SDS (opens in a new tab) — A lower-strength pool acid: 14.5% hydrochloric acid, specific gravity 1.072.
- Leslie’s — Muriatic acid (label directions) (opens in a new tab) — “Never add more than 16 oz per 10,000 gallons at one time.”
- ProPools / Alliance — pH Down (sodium bisulfate) label (opens in a new tab) — Sodium bisulfate 93.2%; dose chart by pH; never more than 1.5 lb per 10,000 gallons at one time.
- Leslie’s — Dry Acid pH Down (opens in a new tab) — 2 lb lowers total alkalinity by 10 ppm in 10,000 gallons; 15 oz for pH 7.6–7.8, 20 oz for 7.8–8.0.
- USGS — Alkalinity calculator: methods (opens in a new tab) — Temperature-dependent equilibrium constants for water and carbonic acid (after Stumm & Morgan), with activity corrections.
- CDC — Model Aquatic Health Code, 5th edition (2024), annex (opens in a new tab) — CYA reduces chlorine’s effectiveness; correcting total alkalinity for CYA by subtracting CYA ÷ 3.
- CDC Healthy Swimming — Home pool and hot tub water treatment and testing (opens in a new tab) — pH 7.0–7.8; free chlorine at least 1 ppm in pools (2 ppm with cyanuric acid) and 3 ppm in hot tubs; no CYA in hot tubs; test twice a day.
- CDC — Pool chemical injuries press release (2014) (opens in a new tab) — Never mix pool chemicals, especially chlorine products with acid; add chemical to water, never water to chemical.
- CDC — Pool chemical safety: storage poster (opens in a new tab) — Separate acid and chlorine; don’t mix different types of chlorine; keep chemicals cool, dry and in original containers.