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Pool pH Calculator
Type your pH reading and get the acid to bring it down or the soda ash to bring it up.
1 of 2: your gallons
Your dose appears here after the last question.
- 7.4 to 7.6
- ideal pool pH
- 7.2 to 7.8
- safe band
- 8.0 and up
- chlorine loses most of its strength
Type in your test result and your pool's volume, and a pool pH calculator tells you exactly how much to add: muriatic acid if the pH needs to come down, or soda ash if it needs to go up.
- pH to aim for: 7.4 to 7.6
- Anything in the 7.2 to 7.8 band is fine
- To ease 7.8 back to 7.5, use 9 fl oz of acid per 10,000 gallons
- Soda ash for lifting 7.2 toward 7.5: 1 lb 1 oz of soda ash per 10,000 gallons
Testing your pool's pH
Your strip or kit gives you pH as a number, typically falling somewhere in the area of 6.8 to 8.2. Anything between 7.2 and 7.8 is okay. Beyond those lines, plan on making an adjustment.
Test total alkalinity before dosing anything. Alkalinity is what keeps your pH from bouncing around, and you want it at 80 to 120 ppm. Ppm stands for parts per million, a measure of how much of something is dissolved in the water. It's what your test reads. The acid amounts here work for water with alkalinity in that normal band.
What is the ideal pool pH?
Shoot for 7.4 to 7.6. The usual goal is 7.5, right in the middle. That leaves you some cushion on both sides before the water leaves that good 7.2 to 7.8 band.
Amounts by pool size
The muriatic acid here is the potent liquid kind sold for pools, and the amounts assume the usual 31.45% strength. Soda ash is a powder, and it pushes pH upward. These figures are for US gallons.
| Pool volume | Muriatic acid (7.8 → 7.5) | Soda ash (7.2 → 7.5) |
|---|---|---|
| 5,000-gallon pools | 4.5 fl oz | Half of 1 lb 1 oz |
| 10,000-gallon pools | 9 fl oz, or 270 mL | 1 lb 1 oz (495 g) |
| 20,000-gallon pools | 18 fl oz | 2 lb 2 oz |
A starting pH that's further from 7.5 calls for more than these amounts.
Adding the chemicals safely
- 1. Run the pump while you work, and leave it on, so the chemical spreads through all the water.
- 2. Pour one chemical at a time, letting it go right into the stream from a return jet.
- 3. Acid goes into water, never the reverse. When diluting acid in a bucket, fill the bucket with water first.
- 4. Never let acid and chlorine meet, not in the pool water, and not in any bucket.
- 5. Give it half an hour once the acid or soda ash is in, then retest. Only add more if the reading still calls for it.
Finding your pool's gallons
Every amount here scales with pool volume, so measure yours carefully. With a typical 4.5-foot average depth, these sizes are common:
- A 12 x 24 ft pool holds roughly 9,690 gallons
- A 16 x 32 ft pool holds roughly 17,200 gallons
- A 20 x 40 ft pool holds roughly 26,900 gallons
The math behind it
Take the surface area in square feet and multiply by the average depth in feet. Multiply that answer by 7.48. For a pool with a slope, add the shallow end depth to the deep end depth, then split it in half for the average. For round and oval pools, swap 5.9 in for 7.48.
As a formula: volume = length × width × average depth × 7.48.
Acid to lower pH to 7.5
| pH now | 10,000 gal | 15,000 gal | 20,000 gal | 30,000 gal |
|---|---|---|---|---|
| 7.8 | 9 fl oz | 14 fl oz | 18 fl oz | 27 fl oz |
| 8.0 | 13 fl oz | 19 fl oz | 26 fl oz | 39 fl oz |
| 8.2 | 16 fl oz | 24 fl oz | 32 fl oz | 48 fl oz |
| 8.4 | 19 fl oz | 28 fl oz | 37 fl oz | 56 fl oz |
Questions people ask
Is a pH of 7.5 too high?
No. 7.5 sits right in the middle of the 7.4 to 7.6 ideal range, so leave it alone.
How much acid does a 20,000 gallon pool need to lower pH?
For a drop from 7.8 to 7.5, roughly 18 fl oz of muriatic acid at 31.45% strength does it. That's with alkalinity in the normal range. A 15,000 gallon pool needs closer to 14 fl oz.
Should I use baking soda to raise pH?
Pool owners reach for baking soda when total alkalinity is low, not as a pH dose. Around 1 lb 6 oz (635 g) bumps alkalinity up by 10 ppm in 10,000 gallons. For pH itself, the amounts on this page are soda ash.
Does muriatic acid also lower alkalinity?
It does. Dropping alkalinity by 10 ppm takes roughly 26 fluid ounces (755 mL) of the 31.45% muriatic acid for every 10,000 gallons of water, well above what a pH dose usually runs.