How does high pH affect the availability of HOCl and HOBr?

High pH significantly affects the availability of hypochlorous acid (HOCl) and hypobromous acid (HOBr), which are key disinfectants in pool water. As the pH level increases, the equilibrium between the acid form (HOCl or HOBr) and the ionized form (OCl⁻ for chlorine or OBr⁻ for bromine) shifts. At higher pH levels, more of the chlorine or bromine becomes ionized, leading to a reduction in the concentration of the more effective disinfecting species (HOCl and HOBr).

HOCl and HOBr are much more effective at lower pH levels because they remain in their undissociated (non-ionic) forms, which have strong oxidizing properties and can easily penetrate microorganisms to inactivate them. Conversely, as the pH rises above the ideal range (typically around pH 7.2 to 7.6 for swimming pools), the effectiveness of these acids diminishes, reducing their availability in the water. In summary, an increased pH reduces the concentration and efficacy of HOCl and HOBr, making them less available for disinfection purposes.