Both numbers are off. Which one do you fix first?
The short answer: alkalinity first, then pH, then calcium hardness. That is Taylor Technologies' order, and it notes that adjusting alkalinity affects pH, so you retest after each change. HTH's pH Down label says the same: adjust alkalinity first to help prevent pH drift.
Part of: Pool pH and Alkalinity: How They Work Together, our overview of every pH and alkalinity fix.
Why alkalinity comes first
Alkalinity is the buffer that holds pH in place (Better Health Channel, TroubleFreePool). If you fix pH while alkalinity is far off, pH moves again: low alkalinity lets it swing, high alkalinity pushes it back up (TroubleFreePool). Raising alkalinity can also raise pH (Better Health Channel), so the pH reading you need is the one after the alkalinity fix.
In practice
| Your test | Order |
|---|---|
| Both low | Baking soda for alkalinity, retest, then raise pH only if still low (raise alkalinity) |
| Both high | One step: acid lowers both (lower alkalinity). Dose by the label of your acid, and retest before any next step |
| Alkalinity high, pH low | Acid for alkalinity, then aeration for pH (high alkalinity, normal pH) |
| Alkalinity low, pH high | Baking soda first, retest, then a small acid dose (our reading of the order) |
And chlorine?
Balance alkalinity and pH before you shock: HTH's shock directions say to test and adjust total alkalinity and pH first. Keep normal chlorine in range throughout; the CDC's minimum is 1 ppm, or 2 ppm with stabilizer.
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Test kit A test kit that reads pH and total alkalinityEvery step on this page starts and ends with a test. A drop-based (liquid) kit or test strips both work; follow the kit's own instructions.
Sources
- Taylor Technologies: LSI calculator (order: alkalinity, pH, calcium; retest after each change)
- HTH Pool Care pH Down (read 3 Nov 2026) (adjust alkalinity first to prevent pH drift)
- HTH Pool Care Shock Advanced (read 3 Nov 2026) (balance alkalinity and pH before shocking)
- Better Health Channel (Victoria State Government): Swimming pools, water quality (raising alkalinity can raise pH)
- TroubleFreePool: ABCs of pool water chemistry (alkalinity stabilizes pH)
- CDC: Home pool and hot tub water treatment and testing (chlorine minimums)
Sources read on November 4, 2026. Product labels change: the label on the product you buy always wins.
