What Is That Smell, Actually?

The sharp, eye-burning smell at poorly maintained pools is chloramines — chemical compounds formed when free chlorine reacts with ammonia introduced by swimmers.

Where does the ammonia come from? Sweat. Urine. Lotions. Body oils. Every swimmer who enters without showering first brings a nitrogen load into the water.

When free chlorine bonds with ammonia, it forms combined chlorine (chloramines). Combined chlorine is largely ineffective as a disinfectant. It also off-gases — which is why indoor pools with poor ventilation smell worse than outdoor ones.

A strong pool smell = low free chlorine, high combined chlorine. Not the reverse.

Why This Matters for Operators

Because the wrong diagnosis leads to the wrong fix. Operators who think the smell means too much chlorine will reduce their dose — exactly the wrong move. A pool that smells like chlorine needs more free chlorine: breakpoint chlorination.

Breakpoint chlorination means adding enough free chlorine to oxidize the combined chlorine completely. The math: dose at roughly 10 times the combined chlorine reading to break through it.

How Do You Know If You Have a Chloramine Problem?

Test for it directly. A standard DPD test kit gives you:

If your CC is above 0.2 ppm, you have a chloramine buildup. Above 0.5 ppm with sharp air smell = your swimmers are noticing.

What Should Operators Do?

  1. Test total and free chlorine every day. Not just free.
  2. Calculate combined chlorine and set a threshold for action (0.4 ppm as your trigger).
  3. Superchlorinate when you hit that threshold — schedule for low-use hours.
  4. Address the source. Mandatory pre-swim showers cut your chloramine load significantly.
  5. Check ventilation. Indoor smell problems are often HVAC problems first.

The CPO course covers all of this in detail. If you're managing a facility and you don't have your certification yet, that's the fastest way to close the gap.