Combined Chlorine
Combined chlorine is the portion of total chlorine that has reacted with nitrogen compounds and is no longer an effective sanitiser.
Definition
Combined chlorine is the portion of total chlorine that has reacted with nitrogen compounds and is no longer an effective sanitiser.
Typical Values: Target: 0 ppm; Action threshold: 0.5 ppm; Calculated as: Total Chlorine minus Free Chlorine
In Plain Language
Combined chlorine consists primarily of chloramines — compounds formed when free chlorine reacts with ammonia and organic nitrogen from bathers. Chloramines are 40–80 times weaker than free chlorine as disinfectants. They are also the primary cause of the characteristic pool smell and eye irritation often mistakenly attributed to too much chlorine.
Why It Matters
Combined chlorine above 0.5 ppm indicates a need for shock treatment. It signals that free chlorine is being depleted faster than it can sanitise.
Typical Values
Target: 0 ppm; Action threshold: 0.5 ppm; Calculated as: Total Chlorine minus Free Chlorine
Last reviewed: 2026-06-01