About the Pool Alkalinity and pH Calculator
This pool alkalinity and pH calculator works out how much chemical to add to bring total alkalinity (TA) and pH into range. Enter the pool volume, your current and target TA, current and target pH and your cyanuric acid (stabilizer) reading, and it returns the pounds of baking soda to raise TA, the acid needed to lower TA, and the soda ash or acid needed to reach your target pH.
It is meant for pool owners balancing water after opening, after heavy rain or when pH keeps drifting. Total alkalinity is the water’s buffer: it resists pH changes, so the pH dose depends on TA. Rather than a fixed rule of thumb, the pH doses here come from a carbonate-chemistry model that accounts for TA and the buffering of cyanuric acid.
Most pools aim for TA of 60–120 ppm (often 70–90 ppm for salt and stabilized pools) and pH of 7.4–7.8. The model assumes ideal chemistry at about 25°C and ignores borates, so treat results as estimates: add about three-quarters of the dose, circulate for a few hours, retest and finish. Always add acid to water — never water to acid — and handle it with gloves and eye protection.
How to use the pool alkalinity and ph calculator
- 1Test total alkalinity, pH and cyanuric acid with a reliable kit.
- 2Enter your pool volume and the current and target readings.
- 3Choose the acid you use.
- 4Add baking soda or acid for alkalinity first, then circulate for several hours.
- 5Retest pH and add the soda ash or acid shown, in stages.
Formula and method
Total alkalinity is reported in ppm as calcium carbonate, and one equivalent of alkalinity is 50.04 g of CaCO3. Baking soda (sodium bicarbonate, 84.01 g/mol) adds one equivalent per mole, which works out to about 1.4 lb per 10,000 gallons for a 10 ppm rise. Lowering TA uses the same number of equivalents of acid; 31.45% muriatic acid supplies one equivalent per 116 g (about 100 mL).
For pH, the calculator works out the dissolved carbonate from your TA, pH and cyanuric acid using equilibrium constants at 25°C (pK₁ 6.35, pK₂ 10.33, cyanuric acid pKa 6.88). Acid lowers alkalinity without changing dissolved carbonate, so the dose is the difference in alkalinity at the two pH values. Soda ash adds two equivalents and one mole of carbonate per mole, which is solved directly. Real pools vary with temperature, salt and borates, so retest after each dose.
- ΔTA
- Change in total alkalinity, ppm as CaCO3
- DIC
- Dissolved inorganic carbon (carbonate) in the water
- pK
- Equilibrium constants for carbonic and cyanuric acid
Worked examples
Raise TA 60 → 80 ppm and lower pH 7.8 → 7.5 in 15,000 gal
A 20 ppm TA rise in 56,781 liters needs 20 × 56,781 ÷ 50,044 ≈ 22.7 equivalents, or 22.7 × 84 g ≈ 1.9 kg (4.2 lb) of baking soda. Lowering pH from 7.8 to 7.5 at 60 ppm TA and 30 ppm CYA needs about 10.4 fl oz of 31.45% muriatic acid.
Lower TA 140 → 90 ppm in 20,000 gal
Dropping TA by 50 ppm in 75,708 liters needs 50 × 75,708 ÷ 50,044 ≈ 75.6 equivalents of acid — about 8.8 kg of 31.45% muriatic acid, or roughly 256 fl oz (2 gallons). Add it in stages with aeration in between.
Raise pH 7.2 → 7.5 in 10,000 gal with soda ash
At 80 ppm TA with no stabilizer, raising pH by 0.3 needs about 14.2 oz of soda ash in 10,000 gallons, according to the carbonate model. Add about three-quarters, circulate and retest.
Frequently asked questions
How much baking soda raises pool alkalinity?+
About 1.4 lb of baking soda raises total alkalinity by 10 ppm in 10,000 gallons. A 15,000 gallon pool going from 60 to 80 ppm needs about 4.2 lb. Broadcast it over the deep end with the pump running.
What is the difference between alkalinity and pH?+
pH measures how acidic or basic the water is right now, while total alkalinity measures its buffering capacity — how strongly it resists pH changes. Higher TA makes pH steadier but also makes it drift upward and harder to lower.
Should I adjust alkalinity or pH first?+
Adjust total alkalinity first, because it controls how pH behaves. Once TA is in range and has circulated for several hours, retest and fine-tune pH with acid or soda ash.
How do I lower alkalinity without lowering pH too much?+
Add acid to bring pH down to about 7.0–7.2, which converts some alkalinity to carbon dioxide, then aerate with jets, fountains or a waterfall. Aeration drives off CO2 and raises pH again without restoring TA. Repeat until TA reaches target.
What should my pool alkalinity be?+
A common target is 80–120 ppm for chlorine pools using cal-hypo or liquid chlorine, and about 60–90 ppm for saltwater pools and pools with stabilizer, where lower TA helps reduce pH drift.