pH Control

pH Control

The pH is a measure of the acidity of the water.

The pH scale goes from 0 to 14, where pH 7 is neutral. If the pH is above 7, the water is basic; if it is below 7 the water is acid. The optimum pH for pool water is 7.4, since this is the same as the pH in human eyes and mucous membranes. A pH of 7.4 also gives good chlorine disinfection.

pH higher than  7
= basic water

pH lower than  7
= acidic water

pH  7.4
= optimal

A high pH gives:
– poorer chlorine disinfection
– skin irritation
– lime precipitation
– cloudiness


A low pH gives:
– aggressive water, which damages the mechanical components of the pool
– irritations of the eyes and mucous membranes
– damage to the pool liner


The guideline pH figure is 7.2 – 7.6. To lower the pH, use sodium bisulphate; to raise it use sodium carbonate.