When you add chlorine to a pool, it doesn't stay in one form. It splits into two categories:
Total chlorine = Free chlorine + Combined chlorine.
Most pool test kits measure all three. The one that matters most for daily management is free chlorine.
Here is the mistake most pool owners make: they see a high total chlorine reading, assume the pool is well-sanitized, and stop adding chlorine. But if most of that total chlorine is combined chlorine, the pool is actually under-sanitized.
Combined chlorine (chloramines) forms when free chlorine reacts with nitrogen compounds — ammonia from sweat, urine, and sunscreen. Once chlorine is "combined," it barely kills anything. Worse, it produces the eye-burning, skin-irritating, pool-smelling compounds that make people think the pool has "too much chlorine."
The chlorine smell you hate is not from too much chlorine — it is from too little. Chloramines cause that smell. A properly maintained pool smells like almost nothing.
| Parameter | Target Range | Notes |
|---|---|---|
| Free Chlorine (FC) | 1–3 ppm | Never let it drop below 1 ppm |
| Combined Chlorine (CC) | Below 0.2 ppm | Above 0.4 = time to shock |
| Total Chlorine (TC) | FC + CC | Should be close to FC reading |
Your test kit may not directly report combined chlorine. Calculate it yourself:
The fix is breakpoint chlorination — also called shocking. You need to raise free chlorine to roughly 10 times the combined chlorine level to oxidize the chloramines and break them apart. At that point the combined chlorine converts back to gas and exits the pool.
For example, if combined chlorine is 0.8 ppm, you need to raise free chlorine to about 8 ppm. Most shock treatments target 10 ppm free chlorine to ensure breakpoint is reached.
After shocking, run the pump and allow free chlorine to drop back to 1–3 ppm before swimming. This usually takes 8–24 hours.
Not all test kits are equal:
If your test strips only show one reading and you do not know which it is, switch to a DPD drop kit or take a water sample to your pool store.
Log free chlorine, combined chlorine, and all your other readings in one place. SplashLens flags when your CC is too high and tells you exactly how much shock to add.
Open SplashLens Free →Free chlorine should be between 1 and 3 ppm for a residential pool. The CDC recommends a minimum of 1 ppm. Never let free chlorine drop below 1 ppm — the pool is unsafe at that point.
Combined chlorine (chloramines) forms when free chlorine reacts with ammonia from sweat, urine, and body oils. Chloramines are a poor sanitizer, cause that strong chlorine smell, and irritate eyes and skin. Calculate it by subtracting free chlorine from total chlorine.
Shock (superchlorinate) your pool. You need to raise free chlorine to about 10 times the combined chlorine level to reach breakpoint chlorination and oxidize the chloramines away.
No. A strong chlorine smell almost always means too many chloramines — not too much free chlorine. A properly balanced pool has almost no odor. The smell is a sign the pool needs shock treatment.
Yes — total chlorine is always equal to or higher than free chlorine because it includes combined chlorine. If the gap is large (more than 0.4 ppm), your combined chlorine is high and you need to shock the pool.