Soda Ash pH Calculator

The dose is a linear rule of thumb: the amount of soda ash scales with your pool volume and the pH gap, then adjusts for product purity.

doseOz = (targetPh - currentPh) / 0.2
         x doseRate
         x (volumeGal / 10,000)
         x (100 / purityPct)

Coupled TA rise (stoichiometric, not buffer-dependent):
  taPpm = (targetPh - currentPh) / 0.2 x doseRate x 0.707
        (volume cancels: the TA rise depends only on the pH gap and the dose rate)

Per-addition cap (label cap is per 10,000 gal, scaled to your pool):
  scaledCap = capOz x (volumeGal / 10,000)
  additions = ceil(doseOz / scaledCap)

Worked example. A 15,000-gallon pool at pH 7.2, target 7.5, using the default 6 oz rate at 100% purity: steps = 0.3 / 0.2 = 1.5; dose = 1.5 x 6 x 1.5 = 13.5 oz; coupled TA rise = 1.5 x 6 x 0.707 = ~6.4 ppm.

Why the dose rate is an editable input, not a fixed constant. Published soda ash dose tables disagree. Swim University cites 6 oz per 10,000 gallons per +0.2 pH for small adjustments; Swim University and the Leslie's Soda Ash pH Up label both give a broader 1 lb (16 oz) per 10,000 gallon rule for pH below 7.2, without stating a pH increment. Our pool chemical dosing calculator treats that same 1 lb per 10,000 gallons as about +0.2 pH. The disagreement is real, not a typo: how much a given weight of soda ash shifts pH depends on the water's current total alkalinity (the buffer). A low-alkalinity pool moves further per ounce than a high-alkalinity one. The default here is 6 oz as a starting point; enter the rate from your product label if it states one, add, wait, and retest.

The coupled alkalinity rise IS a fixed constant. Unlike pH, total alkalinity is a mass balance: each ounce of pure sodium carbonate (Na₂CO₃, 105.99 g/mol) adds 0.707 ppm of CaCO₃-equivalent TA per 10,000 gallons, derived from the molar masses (CaCO₃ = 100.09 g/mol, 1 oz = 28.35 g, 10,000 gal = 37,854 L). That figure does not depend on buffering, so it is asserted as a single number rather than left editable.

Don't know your pool volume? The pool volume calculator works it from shape and dimensions. If you need to lower pH instead of raise it, the mirror tool is the muriatic acid dose calculator. After dosing, read the combined effect of pH, alkalinity and calcium on the Langelier saturation index calculator, which tells you whether the water is etching plaster or scaling the heater. For the full ideal-range picture, see the pool chemistry target chart.

Sources: Swim University (6 oz / 10k / +0.2 pH rule, 1 lb / 10k for pH below 7.2, 4 lb / 10k cap); Leslie's Soda Ash pH Up (1 lb / 10k for pH below 7.2, max 4 lb / 10k per addition). TA coupling constant from PubChem CID 10340 (Na₂CO₃, 105.99 g/mol) and PubChem CID 10112 (CaCO₃, 100.09 g/mol).