Pool pH calculator
How much acid it takes to move pH depends mostly on your total alkalinity, the water's buffer. Enter your volume, current and target pH, alkalinity and stabilizer, and the calculator estimates the dose of acid to lower pH or soda ash to raise it.
What pH to aim for
The CDC recommends keeping pool pH between 7.0 and 7.8. Within that range, many pool owners aim for about 7.4–7.6: comfortable for eyes and skin, and kind to plaster, metal and vinyl. Chlorine also works better at the lower end of the range. Above 8.0, chlorine becomes noticeably less effective and calcium scale forms more easily. Below 7.0, the water starts to etch plaster and corrode metal.
Why alkalinity changes the dose
Total alkalinity is mostly bicarbonate, which soaks up acid and resists pH changes. Water with 120 ppm alkalinity needs noticeably more acid for the same pH drop than water with 70 ppm. Stabilizer (CYA) also buffers a little. That's why this calculator asks for both, instead of giving a fixed "so many ounces per 10,000 gallons".
The calculation treats the pool as a closed carbonate system: it finds how much bicarbonate and carbonate are in the water at the current pH, then how much acid (or soda ash) moves that balance to the target pH. Cyanurate from the stabilizer is included as a second buffer. It uses typical values for pool water's chemical constants, so it's a planning estimate, not a lab result.
Worked examples
Lowering pH: 15,000 gallons from 7.8 to 7.5
With 90 ppm alkalinity and 40 ppm CYA, the calculator estimates about 14.4 fl oz of 31.45% muriatic acid (425 mL), or about 1.2 lb of dry acid. Alkalinity drops to about 86 ppm.
Raising pH: the same pool from 7.1 to 7.5
About 2.6 lb of soda ash. Soda ash raises alkalinity too, here from 90 to about 109 ppm. If your alkalinity is already high, aeration (see below) raises pH without adding anything.
Adding acid safely
- Wear eye protection and gloves. Open the bottle outdoors, upwind.
- With the pump running, pour the acid slowly into the deep end or in front of a return jet, low over the water so it doesn't splash. Don't pour it into the skimmer.
- Add about three-quarters of the calculated amount, circulate for 30 minutes to an hour, retest, and add the rest if needed.
- Never mix acid with chlorine, in a bucket, a feeder or the skimmer. The two release toxic chlorine gas. If you dilute acid in a bucket of water, always add acid to water, never water to acid.
Raising pH without chemicals
Pool water usually holds more carbon dioxide than the air, and as CO₂ escapes, pH rises. Aerating the water speeds that up: point return jets upward, run waterfalls, fountains or spa spillovers, or use the pool. This raises pH without changing alkalinity. It's the best way to raise pH when alkalinity is already at or above your target.
Why pH keeps rising
Steadily rising pH is common, especially in new plaster pools, saltwater pools and pools with high alkalinity. High alkalinity drives CO₂ out of the water faster, which keeps pushing pH up. Lowering alkalinity to the 60–80 ppm range often slows the rise. The alkalinity calculator and our pH and alkalinity guide explain how.
Frequently asked questions
How much muriatic acid per 10,000 gallons lowers pH by 0.2?
It depends on alkalinity. With no stabilizer, going from 7.8 to 7.6 takes about 4 fl oz of 31.45% acid at 80 ppm alkalinity, and about 6 fl oz at 120 ppm. Enter your numbers above.
Muriatic acid or dry acid?
Both lower pH and alkalinity the same way. Liquid muriatic acid costs less per dose and adds only a little chloride. Dry acid is easier to store and handle, but it adds sulfate, which can build up over the years and affect plaster and some salt cells. Many saltwater cell makers name a sulfate limit in their manuals.
My test shows pH above 8.2. Is that accurate?
Many drop-test kits read pH with phenol red, which tops out around 8.2, and high chlorine (above about 10 ppm) can make the reading appear higher than it really is. If you're shocking, wait for chlorine to fall before trusting the pH reading.