This document discusses the chemistry of swimming pools. It explains that chemical balances, especially chlorine and pH levels, are critical for sanitizing pools and keeping swimmers healthy and equipment undamaged. The "active chemical" used is hypochlorous acid (HClO), which exists in equilibrium with hydrogen ions and hypochlorite ions that is dependent on pH. An ideal pH range is 7.2-7.8 - levels too low or high can allow microbes to survive or chemicals to become too concentrated and harmful. Monitoring these chemical balances is important for safe swimming.