Alkalinity Adjustment Calculator
Calculate the sodium bicarbonate (baking soda) needed to raise pool or spa total alkalinity to your target in ppm.
How it works
Baking soda (lb) = Δppm × gallons × 1.5 × 10⁻⁵ · (1.5 lb per 10,000 gal ≈ +10 ppm TA)
Total alkalinity is the water’s buffering reserve, and sodium bicarbonate (plain baking soda) raises it predictably: about 1.5 pounds per 10,000 gallons lifts alkalinity roughly 10 ppm. That reduces to a single constant — multiply the ppm you want to gain by the gallons and by 1.5 × 10⁻⁵ to get pounds. Keep alkalinity in the 80–120 ppm range: it stabilises pH, so adjusting it before pH is the correct order of operations. Lowering alkalinity is a different job that requires muriatic or dry acid.
Worked example
A 15,000-gallon pool going from 80 to 100 ppm needs 20 ppm: 20 × 15,000 × 1.5 × 10⁻⁵ = 4.5 lb of baking soda, roughly 72 oz.
Frequently asked questions
Baking soda or soda ash?
Sodium bicarbonate (baking soda) raises alkalinity with only a small pH nudge and is what this tool doses. Soda ash (sodium carbonate) is for raising pH and pushes alkalinity up sharply as a side effect — use it only when pH is low and alkalinity is fine.
Why adjust alkalinity before pH?
Alkalinity buffers pH, so a pool with the wrong alkalinity fights every pH change. Setting alkalinity into the 80–120 ppm window first makes the subsequent pH adjustment stable and long-lasting.
How do I lower alkalinity?
Add muriatic acid or dry acid (sodium bisulfate), which this raise-only calculator does not cover. Acid lowers both pH and alkalinity, after which you aerate to bring pH back up while alkalinity stays down.
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This calculator is for educational purposes. Double-check important results before acting on them.