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.

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.