Chlorine Demand
Chlorine demand is the total amount of chlorine consumed by all reactions in pool water before a free chlorine residual can be established.
In Plain Language
When pool water has no free chlorine but the addition of chlorine does not produce a residual (FC reads zero immediately after dosing), the water has a high chlorine demand. This can be caused by heavy organic contamination, algae, high combined chlorine, or very high CYA. The demand must be fully satisfied before a free chlorine residual will persist. Reaching breakpoint chlorination satisfies the demand caused by combined chlorine.
Why It Matters
Understanding chlorine demand explains why adding chlorine to some pools seems to produce no results — the demand must be met before residual builds.
Typical Values
Last reviewed: 2026-06-01