How to Lower pH in a Pool
The target range for pool pH is 7.2–7.6. Above that, chlorine loses effectiveness, water turns cloudy, scale forms, and eyes sting. Lowering it takes a measured dose of acid — here is how much, and how to add it safely.
Why high pH is a problem
- •Chlorine works dramatically less well — at pH 8.0, only around a quarter of your free chlorine is in its active sanitising form.
- •Calcium comes out of solution, causing cloudy water and scale on surfaces and equipment.
- •Swimmers notice — high pH is a bigger cause of stinging eyes and dry skin than chlorine itself.
What causes pH to rise
Pool pH drifts upward naturally — carbon dioxide constantly escapes from the water (the same reason soda goes flat), and losing CO₂ raises pH. Anything that agitates the water speeds it up: waterfalls, fountains, spa jets, and heavy swimming. New plaster also raises pH for its first year, and high total alkalinity makes the drift faster and stronger.
How much acid to add
The dose depends on your pool volume and your total alkalinity — alkalinity buffers pH, so the same dose moves low-TA water much further than high-TA water. These figures assume TA around 100 ppm, per 10,000 gallons:
Double the dose for 20,000 gallons; halve it for 5,000. If your alkalinity is well above or below 100 ppm, the dose changes — the PoolScan calculator adjusts for it automatically.
Which acid to use
Dry acid (sodium bisulphate)
Granular and easier to handle, store, and measure — the better choice for most home pool owners. Broadcast slowly across the deep end with the pump running, or pre-dissolve in a bucket.
Muriatic acid (31.45%)
Cheaper per dose and adds nothing to the water but acid — but it is a strong liquid acid that fumes. Work outdoors, wear gloves and eye protection, and dilute in a bucket of water first.
How to add it
- 1Test pH and alkalinity first. Scan your test strip →
- 2Calculate the dose for your volume and alkalinity. Use the PoolScan calculator →
- 3Dilute in a bucket of pool water — always add acid to water, never water to acid.
- 4Pour slowly near a return jet with the pump running. Keep your face averted and avoid inhaling fumes.
- 5Run the pump for at least an hour, then retest. Wait before swimming — retest pH first.
- 6Still high? Re-dose based on the new reading. Never add back-to-back doses without retesting — overshooting into low pH is corrosive to equipment and surfaces.
pH keeps creeping back up?
If you lower pH and it climbs back within days, your total alkalinity is probably too high. High TA acts like a spring pushing pH upward — you cannot win by dosing pH alone. The fix is to lower alkalinity first (also done with acid, added differently), then pH stays put. The target TA range is 80–120 ppm.
This is exactly why the treatment order is alkalinity first, then pH — and why the calculator sorts doses that way.
Safety
- ⚠Always add acid to water — never water to acid. The reverse can spit and splash concentrated acid.
- ⚠Wear gloves and eye protection with either product. Work outdoors or in good ventilation with muriatic acid.
- ⚠Never mix acid with chlorine products — the reaction releases toxic chlorine gas.
- ⚠Store acid away from chlorine, in original containers, out of reach of children.
PoolScan calculates your exact acid dose from your pool volume, pH, and alkalinity readings.
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