Potential hydrogen. pH is a measurement of the level of acidity or alkalinity in the water; it uses a scale of 0 to 15. Metal corrosion, eye irritation, and etched plaster all occur with a low pH. Chlorine inefficiency and scale formation are symptoms of a high pH.
The pool water’s pH had to remain in the 7.4 to 7.6 range to provide the best swimming conditions.