⚠️ Muriatic Acid (31.45%)
liquid hydrochloric acid, 31.45% (20° Baumé) · updated August 2026
Quick answer: add 10 fl oz per 10,000 gallons to lower pH by ~0.2 (at TA ≈ 100 ppm). Add ½–⅔ first, circulate, retest.
Safety — read first
- • ALWAYS add acid to water, never water to acid.
- • Never mix with chlorine — releases toxic gas.
- • Wear eye protection; pour slowly into the deep end away from walls, pump running.
The pH (and alkalinity) reducer. Cheap and effective, but the most dangerous bottle on your shelf — the safety rules are not optional.
Side effects: Also lowers alkalinity (~26 fl oz per 10k gal drops TA 10 ppm) — that's how you lower TA on purpose.
Dosing chart
| Pool size | 0.1 pH | 0.2 pH | 0.3 pH | 0.5 pH |
|---|---|---|---|---|
| 5,000 gal | 2.5 fl oz | 5.0 fl oz | 7.5 fl oz | 12.5 fl oz |
| 10,000 gal | 5.0 fl oz | 10.0 fl oz | 15.0 fl oz | 25.0 fl oz |
| 15,000 gal | 7.5 fl oz | 15.0 fl oz | 22.5 fl oz | 1.2 qt |
| 20,000 gal | 10.0 fl oz | 20.0 fl oz | 30.0 fl oz | 1.6 qt |
| 30,000 gal | 15.0 fl oz | 30.0 fl oz | 1.4 qt | 2.3 qt |
pH dosing is non-linear — the response depends heavily on your total alkalinity. These figures assume TA ≈ 100 ppm; add ⅔ of the dose and retest after 4–6 hours.
FAQ
How much muriatic acid do I add per 10,000 gallons?+
10 fl oz per 10,000 gallons will lower pH by ~0.2 (at TA ≈ 100 ppm). Scale linearly with your pool size — the chart on this page covers 5,000 to 30,000 gallons. pH response depends on your alkalinity, so treat this as a starting point and retest.
What does muriatic acid do to a pool?+
The pH (and alkalinity) reducer. Cheap and effective, but the most dangerous bottle on your shelf — the safety rules are not optional. Side effect to know: Also lowers alkalinity (~26 fl oz per 10k gal drops TA 10 ppm) — that's how you lower TA on purpose.
Is muriatic acid safe to handle?+
ALWAYS add acid to water, never water to acid. Never mix with chlorine — releases toxic gas. Wear eye protection; pour slowly into the deep end away from walls, pump running.