What is the impact of high pH on chlorine efficiency?

High pH levels in pool water can significantly reduce chlorine's ability to disinfect effectively. When the pH is elevated, it increases the amount of hypochlorite ion (OCl-) in relation to hypochlorous acid (HOCl). Hypochlorous acid is the more effective form of chlorine for disinfection purposes. At high pH levels, less chlorine is in the form of hypochlorous acid, which means that the overall sanitizing power of the chlorine diminishes.

The ideal pH range for pool water is typically between 7.2 and 7.8. Maintaining pH within this range ensures that a higher proportion of free chlorine is present as hypochlorous acid, maximizing its efficacy against pathogens. When the pH rises above this optimal range, the shift in the chemical equilibrium leads to reduced disinfection potential, making it harder for the chlorine to kill bacteria, viruses, and other harmful microorganisms that can proliferate in pool water.