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Free tool

Pool pH Calculator

How much acid or soda ash to add, adjusted for your alkalinity.

How these numbers are worked out, and the sources behind them: see our methodology. Updated .

Ideal pool pH

Aim for 7.4 to 7.6. Anything from 7.2 to 7.8 is acceptable.

6.8
7.0
7.2
7.4
7.6
7.8
8.0
8.2

Red: fix now. Amber: acceptable. Green: ideal.

Signs your pH is off

  • High pH (above 7.8): cloudy water, scale at the waterline, chlorine that works poorly, a crusty salt cell.
  • Low pH (below 7.2): stinging eyes, itchy skin, etched plaster, corroded ladders and heater parts.

Why pH keeps rising

Carbon dioxide gassing out of the water pushes pH up. Anything that splashes or aerates speeds that up: waterfalls, spillovers, jets and swimmers. Salt cells make it worse, because generating chlorine raises pH, and new plaster raises it for months. High alkalinity is the fuel: above about 120 ppm, pH climbs every few days. Lowering alkalinity is often the real fix. Read more in why pool pH bounces, how to lower pool pH and how to raise pool pH.

pH, alkalinity and LSI

Alkalinity is the buffer that holds pH in place: low TA lets pH swing, high TA drags it up. pH and alkalinity are also two of the four inputs to the Langelier Saturation Index, which tells you whether the water will etch or scale. Balance alkalinity with the total alkalinity calculator, then check the whole picture with the LSI calculator.

Worked examples

Lowering: a 20,000 gallon pool at pH 8.0 with alkalinity at 100 ppm, target 7.5. That is a 0.5 drop: 32 fl oz x 2 (for 20,000 gal) x 2.5 (for 0.5) = 160 fl oz, about 1.25 gallons of 31.45% muriatic acid. Add it in two halves, 4 hours apart, retesting between.

Raising: a 15,000 gallon pool at pH 7.0 with alkalinity at 80 ppm, target 7.4. 6 oz x 1.5 x 2 = 18 oz of soda ash, times 0.8 for the lower alkalinity: about 14 oz.

pH dose chart per 10,000 gallons

At about 100 ppm alkalinity
Product0.2 pH0.4 pH0.6 pH
Muriatic acid 31.45% (lower)32 fl oz64 fl oz96 fl oz
Dry acid (lower)1.5 lb3 lb4.5 lb
Soda ash (raise)6 oz12 oz18 oz
Borax (raise)12 oz24 oz36 oz
How to use this calculator
  1. 1
    Test pH and alkalinity

    Alkalinity sets how much product it takes to move pH, so enter both.

  2. 2
    Choose raise or lower and your product

    Soda ash or borax raises pH. Muriatic acid or dry acid lowers it. Pick your acid strength.

  3. 3
    Add it safely

    Add acid to water, never water to acid. Pour slowly in front of a return jet with the pump running.

  4. 4
    Split big doses

    Over about 1 quart of acid per 10,000 gallons, add half, wait 4 hours and retest.

  5. 5
    Retest in 4 to 6 hours

    Let the pump circulate, then retest before adding more.

More free tools
Total Alkalinity Calculator

Fix alkalinity first and pH stops drifting.

LSI Calculator

See if pH, alkalinity and calcium add up to balanced water.

Pool Chemical Calculator (all-in-one)

Adjusting more than pH? Get every dose in one plan.

Pool Volume Calculator

Don't know your pool's gallons yet? Start here.

Pool Chlorine Calculator

Balance pH before or after a chlorine dose.

More pool calculators →
Frequently asked

Questions about pool pH

Does total alkalinity affect this calculation?
Yes. Alkalinity buffers pH, so the higher your TA, the more product it takes to move pH the same amount. The calculator scales the dose by about TA/100 and warns you when TA is below 60 or above 150 ppm.
Should I add all the chemical at once?
No. Add it gradually, let the pump circulate for a few hours, then retest before adding more. A big dose of muriatic acid all at once can overshoot your target and stress pool surfaces.
What's the difference between muriatic acid and dry acid?
Both lower pH. Muriatic acid is a liquid dosed by volume; dry acid (sodium bisulfate) is a granular powder dosed by weight. Dry acid is easier to handle and store but costs more per treatment, and it adds sulfates that build up over time.
Can soda ash raise total alkalinity too?
Yes. Soda ash raises pH and also raises alkalinity a little, about 11 ppm per pound in 10,000 gallons. If alkalinity is already high, use borax, which raises pH without moving TA much.
How long after adding acid can I swim?
Once it has mixed, usually 30 minutes to an hour with the pump running. Retest pH first; swim when it reads 7.2 to 7.8.
How much muriatic acid lowers pH by 0.2?
About 1 quart (32 fl oz) of 31.45% muriatic acid per 10,000 gallons at 100 ppm alkalinity. Use more at higher alkalinity and less at lower, and double it for 14.5% acid.
Baking soda vs soda ash: which raises pH?
Soda ash (sodium carbonate) raises pH. Baking soda (sodium bicarbonate) mainly raises alkalinity and barely moves pH. Use baking soda when TA is low, soda ash when only pH is low.
Why won't my pH go up?
Usually alkalinity is very low, so the soda ash is used up buffering instead of moving pH, or the test is reading wrong because chlorine is above 10 ppm. Raise TA first, then pH.