Pool pH Calculator

How to use the pool pH calculator

Enter your gallons, current pH, target pH, total alkalinity and stabilizer (CYA), and pick your acid strength. If the target is lower than the current reading, the calculator returns fluid ounces of muriatic acid. If it is higher, it returns ounces of soda ash and the alkalinity that dose will add. Accepted pH values run from 6.0 to 9.0, with targets between 6.8 and 8.2.

Use a target of 7.4–7.6 for most pools. The CDC’s home pool guidance explains the trade-off: as pH rises, chlorine kills germs less effectively, especially above 8.0, and as pH falls below 7.0, pipes and equipment corrode faster.

Why does the acid dose depend on alkalinity and CYA?

pH measures acidity, but alkalinity and stabilizer are buffers that soak up acid before pH moves. The more buffer in the water, the more acid it takes to shift pH by the same amount. That is why a fixed “ounces per 0.1 pH” rule is often wrong, and why this calculator models the carbonate and cyanurate buffers from your actual TA and CYA.

Here is how much 31.45% muriatic acid the calculator gives to move a 15,000-gallon pool from pH 7.9 to 7.5:

Going from TA 60 to TA 120 raises the acid dose by about two-thirds. Stabilizer adds buffering of its own, so the same pool with CYA 80 needs far more acid than an unstabilized one. Borates, if your pool uses them, add still more buffering that this model does not include, which is one more reason to add acid in stages.

Muriatic acid vs dry acid

Both lower pH and alkalinity together. The difference is handling and what stays in the water.

Half-strength muriatic acid (14.5%) is easier to handle but is not exactly half as strong per ounce because its density differs. For the 15,000-gallon example above at TA 90, it takes about 41.4 fl oz instead of 17.7 fl oz. Select the strength you actually bought so the calculator accounts for it. Sulfates from dry acid build up over seasons and can be hard on some plaster and stone, so long-term heavy use favors muriatic acid.

Soda ash vs borax vs baking soda: how to raise pH

Soda ash (sodium carbonate) is the standard way to raise pH. It raises alkalinity too, so the calculator shows that side effect. Example: a 15,000-gallon pool at pH 7.0, TA 80 and CYA 40 needs about 2 lb 12 oz of soda ash to reach 7.4, and that dose adds about 21 ppm of TA.

Your three options compared:

• Soda ash: raises pH strongly and TA moderately. Best when pH is low and TA is normal. Dissolve in a bucket of pool water first; it can cloud the water briefly.
• Borax: raises pH with less TA increase than soda ash. Useful when pH is low but TA is already at the top of its range.
• Baking soda (sodium bicarbonate): raises TA strongly and pH only slightly. Use it when both TA and pH are low; raising TA first often lifts pH enough on its own.

Low pH in a pool with normal TA usually comes from trichlor tablets or from adding too much acid. If trichlor is your main chlorine, expect to keep correcting low pH.

Why is my pool pH always rising?

pH rises mainly because carbon dioxide escapes from the water. Pool water usually holds more dissolved CO2 than the air above it, and anything that churns the surface lets it out. As CO2 leaves, pH climbs, while TA stays put.

Common causes:

• Aeration: waterfalls, spillovers, fountains, jets aimed at the surface and heavy swimming all speed CO2 loss.
• High total alkalinity: more carbonate in the water means more CO2 to lose and a faster rise. Lowering TA toward 60–80 ppm often slows pH drift noticeably.
• New plaster: fresh plaster releases lime (calcium hydroxide) for weeks to months while it cures, pushing pH up steadily.
• Salt chlorinators: the hydrogen bubbles from a salt cell strip CO2 like an aerator, so salt pools tend to drift up faster. Many salt pool owners run TA lower, around 60–80 ppm, for this reason.
• Cal-hypo and soda ash: both are alkaline and raise pH every time you add them.

How to add muriatic acid safely, step by step

Muriatic acid is the most hazardous product most pool owners handle. Its fumes corrode metal and irritate lungs, and splashes burn skin and eyes.

1. Put on chemical-resistant gloves and eye protection, and stand upwind.
2. Run the pump, and make sure no one is in the pool.
3. Measure the dose outdoors. If you pre-dilute, fill a plastic bucket with pool water first, then add the acid to the water. Never add water to acid.
4. Add about half the calculated dose. Pour slowly and low to the surface, in front of a return jet, or walk it along the deep end.
5. Rinse the measuring cup in the pool and keep the acid capped and away from chlorine.
6. Circulate at least 30 minutes, then retest pH.
7. Re-run the calculator with the new reading and add the rest only if needed.

Never let acid and chlorine meet, in a bucket, a scoop or the same spot in the pool: together they release toxic chlorine gas. Wait at least 30 minutes between adding acid and adding chlorine.

Common pH mistakes

• Chasing pH while ignoring TA. If TA is high, pH will keep rising no matter how often you add acid.
• Dumping the full dose at once. The model is an estimate; buffers vary from pool to pool.
• Testing pH with very high chlorine. Free chlorine above about 10 ppm can bleach some pH reagents and give a false reading.
• Dropping pH below 7.0. Low pH etches plaster and corrodes heaters and ladders.

Check pH alongside your other readings with the pool chemical calculator, and compare all your numbers with the ideal pool water chemistry levels. The full buffer model is explained on the calculator formulas and sources page.