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Why alkalinity changes the amount of acid
Total alkalinity is a buffer: it soaks up acid before the pH moves. The higher your alkalinity, the more acid it takes to lower pH by the same amount. Stabilizer (cyanuric acid) and borates add their own buffering. Simple charts ignore this, so they can be off by a factor of two. This calculator models the carbonate, cyanurate and borate buffers in your water to estimate the dose.
Real pools are never perfectly predictable: temperature, test accuracy and other dissolved substances all play a part. That is why we recommend adding about three quarters of the dose, circulating for at least 30 minutes and retesting before adding the rest.
Raising pH
If your pH is low, you have two options. Soda ash (sodium carbonate, sold as "pH increaser") raises pH quickly but also raises alkalinity. Aeration (fountains, pointing jets upward, running a waterfall) raises pH without adding alkalinity, which is ideal when alkalinity is already high enough. If both pH and alkalinity are low, raise alkalinity first with the alkalinity calculator; pH often follows.
Ideal pH range
| pH | What happens |
|---|---|
| Below 7.0 | Eye and skin irritation, corroded metal, etched plaster and wrinkled vinyl |
| 7.2 – 7.8 | Recommended range (CDC: 7.0–7.8). Most comfortable around 7.4–7.6 |
| Above 7.8 | Chlorine works less effectively, cloudy water and scale |
Safety first: Always read the product label. Add chemicals to water, never water to chemicals. Add one chemical at a time with the pump running, never mix products (especially chlorine and acid), and keep everyone out of the water until levels are back in range. Wear gloves and eye protection when handling acid or shock.
Sources and methodology
Last reviewed: November 2026. Doses are calculated from the chemistry of each product (molecular weights and available chlorine) and cross-checked against manufacturer and industry dosing charts. Recommended ranges follow CDC guidance for home pools and hot tubs.
- CDC – Home pool and hot tub water treatment and testing
- The Pool Nerd – Pool acid calculator (dosing reference)
Frequently asked questions
What should my pool pH be?
Between 7.2 and 7.8, ideally around 7.4–7.6. Below 7.2 the water can irritate eyes and corrode equipment; above 7.8 chlorine works less efficiently and scale can form.
Why does my pH keep going up?
Aeration (waterfalls, spa spillovers, salt cells) and high total alkalinity push pH up over time. Lowering your total alkalinity toward 70–80 ppm usually makes pH much more stable.
Can I add acid and chlorine at the same time?
No. Add them separately, at different points of the pool, with the pump running, and wait at least 30 minutes between them. Never mix acid and chlorine in a bucket: it releases toxic chlorine gas.
Why add only part of the acid first?
Pool water is not perfectly predictable: borates, temperature and test accuracy all shift the result. Adding about three quarters, circulating and retesting avoids overshooting to a pH that is too low.