pH
pH measures the concentration of hydrogen ions in water on a logarithmic scale from 0 (most acidic) to 14 (most alkaline), with 7.
Definition
pH measures the concentration of hydrogen ions in water on a logarithmic scale from 0 (most acidic) to 14 (most alkaline), with 7.0 being neutral.
Typical Values: Pools: 7.2–7.6; Hot tubs: 7.2–7.8; Never above 8.0
In Plain Language
Pool water pH directly controls the proportion of chlorine in its active form (hypochlorous acid). At pH 7.2, approximately 67% of free chlorine is active. At pH 8.0, only 22% is active. pH also affects swimmer comfort (human tears are pH 7.4), surface corrosion (low pH), and scaling (high pH). pH naturally drifts upward in pools as CO2 off-gasses from the water surface.
Why It Matters
Every other water chemistry parameter is affected by pH. It is the master control variable in pool management.
Typical Values
Pools: 7.2–7.6; Hot tubs: 7.2–7.8; Never above 8.0
Last reviewed: 2026-06-01