Pool & spa
Pool pH Calculator
Adjusts pH, the parameter that controls whether everything else works.
Result
Dose against a test result, never against a schedule. Add chemicals in stages with the pump running, wait for a full turnover, then retest before adding more. Never mix chemicals, and never add water to acid. Where a product label differs from the figure here, the label wins. pH dosing is strongly affected by total alkalinity, which acts as a buffer. Low alkalinity makes pH swing wildly and acid overshoot; high alkalinity makes pH stubborn and drift upward. Fix alkalinity before chasing pH. Acid is dangerous: add acid to water, never water to acid, and never mix it with chlorine.
Get a Free Business AuditHow the calculation works
The dose is the gap between current and target pH, scaled by volume and by the water's resistance to change, which is its total alkalinity. That second part is why pH dosing is not a simple linear calculation: alkalinity buffers pH, so water with high alkalinity resists correction and needs more acid to move, while water with very low alkalinity swings unpredictably from small additions. Acid lowers pH, soda ash or similar raises it.
What moves the number
- Current pH against target, which is the gap.
- Total alkalinity, which determines how much the water resists change.
- Volume, which scales the dose.
- What is driving the pH, since a persistent rise has a cause.
Where this one goes wrong
Fix alkalinity before chasing pH. Water with alkalinity outside the sensible range either refuses to move or swings wildly, and an owner adding acid repeatedly to a high alkalinity pool is fighting the buffer rather than the pH. Correct alkalinity first and pH becomes manageable. A persistently rising pH also has causes worth identifying rather than dosing around: aeration from water features and salt chlorine generation both drive pH up, and fresh plaster raises it for months. Add acid diluted and distributed rather than poured in one spot, since concentrated acid damages surfaces and equipment.
Before you quote
- Correct total alkalinity before chasing pH.
- Identify what is driving a persistent pH rise rather than dosing repeatedly.
- Dilute and distribute acid rather than pouring it in one place.
Where the rules come from
Questions
About this calculator
Why does my pH keep rising?
Aeration is the usual cause: fountains, waterfalls and jets drive off carbon dioxide which raises pH. Salt chlorine generators do the same. New plaster also raises pH for months as it cures. Those are causes to manage rather than conditions to dose around indefinitely.
Why won't my pH move when I add acid?
Because total alkalinity is too high and is buffering it. Alkalinity resists pH change, which is its function, so water with a high reading needs a lot of acid to move pH at all. Correcting alkalinity first makes pH manageable with normal doses.
Does pH matter if the chlorine is right?
Very much, because pH determines how much of that chlorine is in the effective sanitising form. High pH leaves chlorine present but far less active, so the reading looks fine while sanitising is poor. It also affects comfort, scaling and corrosion of surfaces and equipment.
The formula
roughly 8 fl oz of 31% muriatic acid per 10,000 gallons lowers pH by about 0.1
Put this calculator on your site
Free to embed. Paste this where you want it to appear. It stays up to date automatically because it loads from BDEVY.
Please keep the attribution line. It is the only thing we ask in return.
How to use this calculator
- Pool volume (gallons). Enter your own figure; the page starts at 20,000.
- Current pH. Enter your own figure; the page starts at 7.8.
- Target pH. Enter your own figure; the page starts at 7.5.
- Price per pound or gallon ($). Enter your own figure; the page starts at $0.08.
The result updates as you type, so you can try a figure, see what it does to muriatic acid to add, and change it back. Nothing you enter is sent anywhere or saved.
A worked example
These are the figures the calculator opens with. Every number in the results column below is produced by the same calculation the page runs, so you can follow it through before putting your own figures in.
What goes in
| Input | Value |
|---|---|
| Pool volume (gallons) | 20,000 |
| Current pH | 7.8 |
| Target pH | 7.5 |
| Price per pound or gallon | $0.08 |
What comes out
| Result | Value |
|---|---|
| Muriatic acid to add main result | 48.0 |
| Change needed | -0.3 |
| Estimated cost | $3.84 |
| Dose per 10,000 gallons | 24.0 |
Add about 48.0 of muriatic acid to bring pH from 7.8 down to 7.5. Add it slowly with the pump running, then retest.
How sensitive the answer is
Holding everything else steady and changing only price per pound or gallon, this is what happens to muriatic acid to add. It is worth knowing which of your inputs the answer actually hinges on, and which barely move it.
| Price per pound or gallon ($) | Muriatic acid to add |
|---|---|
| $0.04 | 48.0 |
| $0.06 | 48.0 |
| $0.08 example above | 48.0 |
| $0.12 | 48.0 |
| $0.16 | 48.0 |
Every other input is held at the example value while this one changes, which is not how a real job behaves. Treat it as a guide to which number matters most, not as five separate quotes.
What each figure means
- Pool volume (gallons)
- A number, between 0 and 2000000, starting at 20,000.
- Current pH
- A number, between 0 and 9, starting at 7.8.
- Target pH
- A number, between 0 and 9, starting at 7.5.
- Price per pound or gallon ($)
- A money amount, starting at $0.08.
What the results tell you
| Result | What it is |
|---|---|
| Muriatic acid to add | The headline result. A decimal figure. |
| Change needed | A decimal figure. |
| Estimated cost | A money figure. |
| Dose per 10,000 gallons | A decimal figure. |
Estimating is the easy part
The jobs you never hear about cost more than the ones you mis-measure. BDEVY builds the marketing, systems and automation that bring them in.