Pool pH Adjustment Calculator (Acid / Base)

Target pH is 7.4-7.6. Below 7.0 the pool starts dissolving metal fittings and irritating skin. Above 7.8 chlorine becomes lazy (only ~30% active form at pH 8.0 versus ~75% at pH 7.5). The 7.4-7.6 sweet spot is also closest to human eye pH, which is why eyes do not sting.

To raise pH (pH below 7.4):

• Soda ash (sodium carbonate): the standard. Also raises TA slightly.
• Borax: raises pH with less TA effect, but adds borate to the pool (some people like this, some do not).
• Aeration (no chemical): if TA is high, just running fountains for hours raises pH naturally as CO₂ outgases.

To lower pH (pH above 7.6):

• Muriatic acid (hydrochloric acid, ~31.45%): the standard. Lowers both pH and TA.
• Dry acid (sodium bisulfate): same effect as muriatic, easier to handle, but adds sulfate ions over time.
• CO₂ injection: commercial pools mostly. Lowers pH without lowering TA.

Why TA affects the dose. Total alkalinity buffers pH change. A pool with TA 120 needs roughly twice as much acid to drop pH by 0.2 as a pool with TA 60. The calculator factors this in using a standard buffer ratio.

Reference doses (per 10,000 gal, per 0.2 pH change, at TA 100):

• Soda ash: 6 oz raises pH by 0.2 (raises TA by ~5)
• Borax: 11 oz raises pH by 0.2 (no significant TA effect)
• Muriatic acid 31.45%: 16 fl oz lowers pH by 0.2 (lowers TA by ~10)
• Dry acid: 12 oz lowers pH by 0.2 (lowers TA by ~10)

The “add acid in stages” rule. When dropping pH significantly (more than 0.4), add half the calculated dose, run the pump for an hour, retest, then add the rest if needed. Acid doses can over-correct because TA buffers respond on a delay.

Safety. Muriatic acid is corrosive. Always add acid to water (never water to acid), add it in front of a return jet, never near the skimmer, and never add it within 30 minutes of adding chlorine — the gas reaction is no joke.