How much muriatic acid to add to a pool The short answer How much muriatic acid to add depends on your pool size, how far pH has to fall, and your alkalinity — higher alkalinity needs more. About 8 fl oz of 31.45% acid takes 10,000 gallons from pH 7.8 to 7.5 when alkalinity is 80 ppm, and about 11 fl oz when it is 120. The calculator below gives your exact dose, in parts.
How much muriatic 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 Work out the dose with the calculator on this page, for the strength you have (31.45% or 14.5%).
Put on gloves and eye protection. Always add acid to water, never water to acid.
With the pump running, pour it slowly in front of a return jet — never into the skimmer.
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 Muriatic acid is hydrochloric acid: it lowers pH and alkalinity together. The more alkalinity the water has, the more acid the same pH change takes.
Questions 31.45% or 14.5% muriatic acid? The 14.5% kind is half strength: you need about twice as much. The calculator handles both.
Can I add muriatic acid and chlorine at the same time? No. Add one, let it mix with the pump running for at least 30 minutes, then the other. Never mix them outside the pool.
Where do I pour muriatic acid in a pool? Slowly in front of a return jet with the pump running, or along the deep end. Never into the skimmer.
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