Not sure? Use the volume calculator.
To lower pH by 0.3, add
28.8 fl oz (3.6 cups)
muriatic acid 31.45%
Side effect: total alkalinity drops roughly 9 ppm.
Safety first. Always add acid to water, never water to acid. Pour slowly into the deep end with the pump running, away from skimmers and fittings, and never mix acid with chlorine — the gas is dangerous. Wait at least 30 minutes of circulation before retesting.
Why alkalinity changes the dose
Total alkalinity is the water's buffer against pH change — the higher it is, the harder the water resists your acid. The same 0.3 pH drop takes roughly twice the acid at TA 160 as it does at TA 80. That's also why this calculator shows the alkalinity side effect: every acid dose lowers TA along with pH, and on a weekly route those reductions add up.
Practical dosing rules
- Dose in stages. For drops bigger than 0.3, add half, circulate, retest. Overshooting low pH is more damaging (and harder to see) than staying slightly high.
- Mind the LSI. Lowering pH pushes water toward corrosive — sanity-check big adjustments with the LSI calculator.
- Using dry acid? Sodium bisulfate works the same direction; follow the label rate (roughly 1 lb dry acid ≈ 1 qt muriatic in effect) and note it adds sulfates, which salt-cell manufacturers dislike.
- Log every dose — pH drift patterns (new plaster, high-TA fill water, heavy bather load) only show up in history. Tadpole logs doses per stop.
These doses are field estimates from standard industry tables — start conservative, follow the product label, and retest before adding more.
