Calculate My Pool
Units

Pool pH Calculator

Enter pH now, your target, alkalinity and CYA to get the acid or soda ash dose, the alkalinity it will use, and how much TA changes the answer.

Units
gal

Total water in the pool, not the size of the shell.

Don't know your gallons? Calculate it
Shape
ft
ft
ft

Shallow end plus deep end, divided by two. About 4.5 ft (1.4 m) for a typical backyard pool.

About 19,150 gal (72,491 L)

PHTA ideal 7.4 to 7.6.

ppm

The buffer: the higher it is, the more acid each 0.1 of pH costs.

ppm

CYA also buffers pH, so it changes the dose.

2.6 fl oz in 10,000 gal lowers TA by 1 ppm. hydrochloric acid by weight, 20 Baume, density 1.157 g/mL.

Lower pH from 7.9 to 7.5

16.4fl oz Muriatic acid 31.45% (20 Baume)

Same as 486 mL, 2.1 cups.Buy: 1 x 1 gal jug.About 4.3 ppm of TA is used up: TA goes from 80 to about 76 ppm. This is a model, so dose in parts, run the pump and retest.
TA after
76ppm
Additions
1
pH now7.9 high
6.6ideal 7.4 to 7.68.4
TA now80 ppm in range
0ideal 80 to 100 ppm200

pH versus TA: the same target at other alkalinities

  • If TA were 60 ppm13.2 fl oz
  • If TA were 80 ppm16.4 fl oz
  • If TA were 100 ppm19.6 fl oz
  • If TA were 120 ppm22.9 fl oz

Same pool, pH and CYA. High TA holds pH up, so it takes more acid to move it; fix TA first when both are off (see the alkalinity calculator).

Acid to buy

15,000 gal (56,781 L), pH 7.9 to 7.5, TA 80, CYA 40

QuantityItem
1pack

Muriatic acid 31.45% (20 Baume), 1 gal jug

Dose 16.4 fl oz (486 mL)

The math

  1. Alkalinity to remove

    carbonate + cyanurate buffer at TA 80 ppm, CYA 40 ppm, pH 7.9 to 7.5 = 4.3 ppm

  2. Product

    4.3 ppm × 15,000 gal (56,781 L) × product per ppm = 16.4 fl oz

Published label doses give one number per 0.1 to 0.2 of pH, but the real dose depends on your buffering, which is why this page asks for TA and CYA. The model treats the pool as a closed jar of water; aeration and chlorine additions move pH as well.
Before you pour: never mix chlorine and acid, and never mix different chlorine products. Add chemicals to the water, never water to chemicals. Add one product at a time, run the pump, and retest after the water has circulated. Follow the label of the product you bought if it differs.

For a 15,000 gallon pool at pH 7.9 with total alkalinity (TA) 80 ppm and cyanuric acid (CYA) 40 ppm, bringing pH down to 7.5 takes about 16.4 fl oz of 31.45% muriatic acid (2.1 cups, 486 mL). The same pool with TA 120 ppm needs 22.9 fl oz for the same move. Enter your own pH, target, TA and CYA above: the dose depends on all of them, which is why a fixed "6 ounces per 0.1" chart is only a rough guide.

How the pH dose is calculated

pH does not move in a straight line with acid. Alkalinity, mostly bicarbonate, plus cyanurate from CYA, is the buffer that resists change. The calculator solves the carbonate and cyanurate equilibrium for the amount of acid that leaves the pool at your target pH, then converts the acid equivalents into product.

Acid = alkalinity removed for the target pH × gallons ÷ 10,000 × acid per ppm of TA

At TA 80, CYA 40, pH 7.9 to 7.5 the buffer model removes 4.3 ppm of TA. At 25.6 fl oz of 31.45% acid per 10 ppm per 10,000 gallons, that is about 4.3 ÷ 10 × 1.5 × 25.6 = 16.4 fl oz. Raising pH is the mirror image with soda ash (sodium carbonate): from pH 7.0 to 7.5 at TA 60 and CYA 40 it takes 2.7 lb and raises TA by 20 ppm.

This is a model, not a lab result. It treats the pool as a closed jar. Real water loses carbon dioxide to the air, and every chlorine dose shifts pH, so the answer is a first dose. Swim University's guide gives 12 to 16 fl oz of muriatic acid per 10,000 gallons for pH 7.6 to 8.0, which is the same order as the model. Other charts run higher, in the range of 6 fl oz per 0.1 pH. Add half of the result, run the pump, retest, and add the rest.

pH versus TA

The table under the result repeats your dose at four alkalinities, holding pH and CYA fixed. In the default pool, TA 60 needs 13.2 fl oz, TA 100 needs 19.6 fl oz and TA 120 needs 22.9 fl oz. High TA holds pH up, so it takes more acid to move it. PHTA says to correct total alkalinity before adjusting pH: if TA is far off, the pool alkalinity calculator is the first stop. Acid also uses up alkalinity, about 4.3 ppm here, so keep an eye on TA if it is already near 60.

The pH target: which range

PHTA and ANSI/APSP-11 call 7.4 to 7.6 ideal and 7.2 to 7.8 acceptable, and the CDC Healthy Swimming pages use the same 7.2 to 7.8. Trouble Free Pool argues for a slightly higher ideal, 7.6 to 7.8 with a floor of 7.2. Our default target is 7.5 in the middle of the PHTA ideal, and the meter above shows your reading against the range.

Why pH drifts

Liquid chlorine has a pH of about 13, and cal-hypo also raises pH, so most pools chlorinated with either drift up. Dichlor lowers it slightly, and trichlor is acidic. Water that is aerated by jets and waterfalls loses carbon dioxide and rises. That is why pool owners often go through acid in summer, and why the pH page cross-checks with alkalinity.

Acid choice and how much at once

Muriatic acid 31.45% (20 Baume), 14.5% and dry acid (sodium bisulfate 94%) are all in the selector. The Indiana State Department of Health guide limits one addition of liquid acid to 1 quart per 10,000 gallons, so a big correction is split into parts. The muriatic acid pool calculator covers the strengths and handling in detail. To raise pH, soda ash is not the same product as baking soda: baking soda is for alkalinity.

Metric

In a 56.8 m³ pool the default dose is 486 mL of 31.45% acid. Switch the toggle to see litres and grams.

What to do next

Check the whole balance with the LSI calculator, adjust chlorine with the pool chlorine calculator, and enter all your readings in the pool chemical calculator. Find your gallons with the pool volume calculator, and see the pool chemistry hub for the other tools.