Pool pH and alkalinity dosing calculator
Alkalinity buffers pH, so adjust alkalinity first. Chasing pH in a low-alkalinity pool is a losing game.
ppm
ppm
%
Acid to lower pH
400mL
- Acid in litres
- 0.400
- Soda ash to raise pH
- 0
- Sodium bicarbonate to raise alkalinity
- 2.040
- Alkalinity increase needed
- 30 ppm
- Alkalinity is in the ideal band 80 to 120 ppm for most pools.
- 0
- pH change required
- 0.40
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- Pool volume = 40 000
- Current pH = 7.8
- Target pH = 7.4
- Current total alkalinity = 70
- Target total alkalinity = 100
- Acid strength = 31.45
- pH change required = 7.8 - 7.4 = 0.4
- Acid to lower pH = 0.4 > 0 ? 40 000/10000 * 0.4 * 250 * (31.45/31.45) : 0 = 400
- Soda ash to raise pH = 0.4 < 0 ? 40 000/10000 * abs(0.4) * 150 : 0 = 0
- Alkalinity increase needed = max(100 - 70, 0) = 30
- bicarb_g = 40 000/10000 * 30 * 17 = 2040
- Sodium bicarbonate to raise alkalinity = 2040 / 1000 = 2.04
- ta_from_bicarb = 40 000 > 0 ? 2040 / (40 000/10000) / 17 : 0 = 30
- Acid in litres = 400 / 1000 = 0.4
- Alkalinity is in the ideal band = 70 >= 80 && 70 <= 120 ? 1 : 0 = 0
Values are shown to six significant figures here; the arithmetic itself runs on exact fractions and is only rounded where a number is printed.
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The formula
- dose scales with pool volume and the size of the change
- sodium bicarbonate raises total alkalinity by about 10 ppm per 17 g per 10 000 litres
Acid lowers both pH and alkalinity; bicarbonate raises both. Aeration raises pH without touching alkalinity, which is how you separate the two.
Add acid slowly with the pump running, and never pour it near the skimmer or a metal fitting.