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How to lower alkalinity in a pool
High alkalinity makes pH climb again and again. The fix is a slow cycle: acid lowers both pH and alkalinity, then aeration brings only the pH back up.
The cycle
- Add acid to bring pH down to about 7.0 to 7.2. Do not go lower.
- Aerate: run fountains and point return jets upward until pH rises to about 7.6 or more.
- Test alkalinity. If it is still high, repeat.
Each round removes some alkalinity for good, while aeration restores the pH. Expect several days.
Total acid for the drop
| Pool size | -20 ppm | -40 ppm | -60 ppm |
|---|---|---|---|
| 5,000 gal | 26 fl oz | 1.6 qt (51 fl oz) | 2.4 qt (77 fl oz) |
| 10,000 gal | 1.6 qt (51 fl oz) | 3.2 qt (102 fl oz) | 1.2 gal (154 fl oz) |
| 15,000 gal | 2.4 qt (77 fl oz) | 1.2 gal (154 fl oz) | 1.8 gal (230 fl oz) |
| 20,000 gal | 3.2 qt (102 fl oz) | 1.6 gal (205 fl oz) | 2.4 gal (307 fl oz) |
| 30,000 gal | 1.2 gal (154 fl oz) | 2.4 gal (307 fl oz) | 3.6 gal (461 fl oz) |
Spread that total over the rounds. Do not pour it all in at once, since that would drop pH far too low and can damage plaster and equipment.
If your fill water is very high in alkalinity, it will creep back. In that case, aim for the top of the range instead of fighting it.
Add chemicals to water, never water to chemicals, one at a time, with the pump running. Wear gloves and eye protection, and never mix products.