About this tool
The Pool pH Adjuster is a free, in-browser tool that estimates how much acid or base to add to move your pool's pH toward a target. If the target is below the current pH it doses muriatic acid (hydrochloric acid, 31.45% / 20° Baumé) to lower it; if the target is higher it doses soda ash (sodium carbonate) to raise it. All calculations run locally in your browser, so your readings stay on your device.
The change needed is delta_pH = |target − current|. To lower pH, the muriatic-acid dose is fl oz = 8 × (gallons / 10,000) × (delta_pH / 0.2) × (TA / 100); the total-alkalinity term matters because alkalinity buffers pH, so a highly buffered pool needs more acid per unit of pH change. To raise pH, the soda-ash dose is oz = 6 × (gallons / 10,000) × (delta_pH / 0.2). Volumes convert to milliliters (× 29.5735) and cups; weights convert to grams (× 28.3495) and pounds.
As a worked example, lowering a 10,000-gallon pool with TA = 100 ppm from pH 7.8 to 7.4 (delta 0.4) needs about 16 fl oz — roughly 473 mL, or 2 cups — of muriatic acid. Add chemicals in half-doses with the pump running, wait about 6 hours, and re-test before adding more, because these agents also shift total alkalinity. If alkalinity is above roughly 120 ppm, correct it before chasing pH.