Most swimming pools and hot tubs should be kept at a pH of about 7.2 to 7.6. In this range chlorine works well, the water feels comfortable on eyes and skin, and equipment is protected from both corrosion and scale.
Why pH matters so much
pH describes how acidic or alkaline the water is, on a scale from 0 to 14, with 7 as neutral. A small change makes a big difference, because the scale is logarithmic: pH 8 is ten times more alkaline than pH 7.
- Sanitiser efficiency: chlorine is much more active at the lower end of the range. At high pH, more chlorine is needed for the same effect.
- Comfort: water that is too acidic or too alkaline irritates eyes and skin.
- Equipment: low pH can corrode metal parts and heaters; high pH encourages scale on surfaces and heater elements.
What makes pH drift
pH is rarely stable on its own. Salt chlorinators and liquid chlorine tend to push it up; bathers, rain and some chemicals change it too. Splashing and aeration – waterfalls, jets, hot tub air blowers – drive off carbon dioxide and raise pH. Total alkalinity acts as a buffer that slows these changes.
How often should pH be checked?
Traditionally, pool owners test once or twice a week and service companies at each visit. In hot tubs and busy pools, pH can move much faster than that. Continuous monitoring with an inline pH probe, such as EVVO Sense, shows the trend and gives an alert before the water drifts far out of range.
Frequently asked questions
What is the ideal pH for a swimming pool?
About 7.2 to 7.6 for most pools. Check local guidance for public and commercial pools.
What happens if pool pH is too high?
Chlorine becomes less effective, the water can turn cloudy, and scale can build up on surfaces and heaters.
What happens if pool pH is too low?
The water can irritate eyes and skin and corrode metal parts, heaters and fittings.
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