Quick answer
Combined chlorine is total chlorine minus free chlorine. It measures chloramines — spent chlorine bound to sweat, urine and other bather waste — which cause the "chlorine smell" and eye irritation. Commercial pools should keep combined chlorine below 0.4 ppm. When it rises, operators breakpoint chlorinate by raising free chlorine to about 10 times the combined chlorine level.
- Combined chlorine = total chlorine − free chlorine.
- Target: below 0.4 ppm (MAHC).
- Breakpoint dose ≈ 10 × combined chlorine, raised as free chlorine.
- Log CC daily and record every breakpoint treatment.
How to calculate breakpoint chlorination
- Test free chlorine (FC) and total chlorine (TC). CC = TC − FC.
- Multiply CC by 10 to find the breakpoint target increase.
- Subtract the current FC to find how much free chlorine to add.
- Convert ppm to product quantity using your pool volume and the product label.
- Add chlorine, circulate, and re-test until CC is below 0.4 ppm.
| Example | Value |
|---|---|
| Free chlorine | 1.5 ppm |
| Total chlorine | 2.1 ppm |
| Combined chlorine | 0.6 ppm |
| Breakpoint target (0.6 × 10) | 6.0 ppm |
| Chlorine to add (6.0 − 1.5) | ≈ 4.5 ppm |
Skip the arithmetic: the breakpoint chlorination calculator does steps 1–4 for your pool volume and chlorine product.
Preventing high combined chlorine
- Enforce pre-swim showers — the single biggest lever.
- Maintain free chlorine consistently rather than in spikes.
- Replace water regularly to dilute accumulated waste.
- Improve indoor air handling for indoor pools.
- Consider supplemental UV or ozone systems where allowed.
Frequently asked questions
What is an acceptable combined chlorine level?
Below 0.4 ppm for commercial pools under the CDC MAHC; many operators aim for 0.2 ppm or less.
How do you lower combined chlorine?
Breakpoint chlorinate by raising free chlorine to about 10 times the combined chlorine reading, and reduce the source of chloramines through showering, water replacement and ventilation.
Does a strong chlorine smell mean too much chlorine?
Usually the opposite. A strong "chlorine" smell comes from chloramines (combined chlorine), which means there is not enough free chlorine to break them down.
This page is an educational summary, not legal advice. Pool and spa codes differ by state and county and change over time — always confirm requirements with the health department that inspects your facility.