Muriatic Acid Dose Calculator

Two published rules of thumb drive the pH dose, and they disagree by about 8× — so we show a range, not a single false-precision number. The conservative chart rule is the headline because under-dosing then re-testing is the safe direction with a corrosive.

Lower pH:
  chart rule (headline) : 0.004 × volumeGal × (currentPh − targetPh)   fl oz
  quart rule (high end) : 0.032 × volumeGal × (currentPh − targetPh)   fl oz
  (8 fl oz / 10k ≈ −0.2 pH   vs   1 qt / 10k ≈ −0.1 pH)

Lower TA:
  dose = 0.0002 × volumeGal × (currentTa − targetTa)   fl oz
       = (20 fl oz / 10,000 gal ≈ −10 ppm TA);   ±10% house band
  coupling: also lowers pH ≈ dose31% / (0.004 × volumeGal)

Strength adjustment (both modes):
  ×(31.45 / yourStrength%)   — a 14.5% jug needs ≈2.17× the 31.45% dose

Every figure assumes 31.45% (20° Baumé) acid, then scales by 31.45 / your strength. A 14.5% home-store jug needs about 2.17× the fluid ounces of pool-store acid — silent 31.45% defaulting would under-dose that user.

In TA mode, muriatic acid lowers both total alkalinity and pH. We estimate the incidental pH drop by inverting the chart pH slope against the 31.45%-equivalent dose, so the coupled pH figure does not change with jug strength. The real pH response is buffered by alkalinity, so treat it as an estimate — add, re-test, repeat.

Acid is rarely the only move. Because the same jug pulls pH and alkalinity together, plan the raise side and the target band on the pool alkalinity calculator before you pour, and read the combined effect of pH, alkalinity and calcium on the Langelier saturation index calculator, which is the check that says whether the water is etching plaster or scaling the heater. The whole balanced set of readings this dose is aiming at sits on the pool chemistry target chart. A drained, off-line acid wash of stained plaster is a different job entirely, priced on the acid wash pricing calculator, and nothing on this page is guidance for handling the acid itself.

Sources: AllInOneCalculator — How Much Muriatic Acid to Add to Your Pool (both rules of thumb, 31.45% basis); poolchemicalcalculator.com (acid-strength list with Baumé degrees). These are industry-standard but approximate constants — which is exactly why v1 emits a range.