How to lower pH in a pool The short answer To lower pH in a pool, add muriatic acid or dry acid (sold as “pH Down”) a little at a time, with the pump running, poured slowly in front of a return jet. About 8 fl oz of 31.45% muriatic acid takes 10,000 gallons from pH 7.8 to 7.5 when alkalinity is 80 ppm. The calculator below works out your pool; higher alkalinity needs more.
How much acid your pool needs pH now
How acidic the water is. Right, chlorine works and eyes do not sting; wrong, it damages the pool.
pH you want
Good range: 7.2–7.8.
Alkalinity (if you know it)
It decides how far a dose moves pH. Empty = a typical 80.
Stabilizer (if you know it)
Stabilizer buffers pH too. Empty = a typical 30.
Using pH up.
Type the size and your pH reading.
Step by step Test pH and alkalinity. The good range is pH 7.2–7.8; aim for about 7.5.
Work out the dose with the calculator on this page, for the acid you have.
Put on gloves and eye protection. Always add acid to water, never water to acid.
With the pump running, pour the acid slowly in front of a return jet — never into the skimmer. A big dose goes in parts.
Wait a few hours, test again, and add the next part only if pH is still high.
The product label always wins — if it says something different, follow the label.
Why it happens pH rises on its own as carbon dioxide leaves the water: fountains, waterfalls, spa spillovers, swimmers and salt chlorine cells all drive it up.
High alkalinity makes pH climb faster. Keeping alkalinity at the low end of its range (60–80 ppm) slows the climb.
Questions Muriatic acid or dry acid — which is better? Both lower pH and alkalinity the same way. Muriatic acid is cheaper and liquid; dry acid is a powder that is easier to store and handle.
Why does my pH keep going up? Aeration and high alkalinity. Bring alkalinity down to the low end of its range and pH drifts up much more slowly.
Can I use vinegar to lower pool pH? It would take gallons of vinegar to do what a cup of pool acid does. Use pool acid.
How long after adding acid can I swim? Once it has mixed in with the pump running — follow the time on your product’s label.
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