A sharp chemical smell hanging over a swimming pool is one of the most common complaints from pool owners — and from families who use them. The conventional explanation is that the smell means too much chlorine. But often there is another explanation.
The smell is not chlorine
Often when pools have a sharp chlorine odour what you're actually smelling is in fact trichloramine — also called nitrogen trichloride — one of a family of compounds known as chloramines.
Chloramines form when chlorine reacts with nitrogen-containing compounds in pool water, primarily urea from urine and sweat. Trichloramine is the most volatile of these compounds, meaning it evaporates readily into the air above the water surface. It is also the most irritating.
A strong pool smell is a sign of high chloramine levels, not necessarily high chlorine levels. Chloramines form when chlorine is consumed reacting with organic matter.
Why adding more chlorine doesn't fix it
The standard advice — add more chlorine, or "shock" the pool — can temporarily reduce chloramine levels by oxidising them. But the underlying problem remains: as long as people are swimming in the pool, the nitrogen compounds that feed chloramine formation keep entering the water. Chloramines re-form continuously, and the smell returns.
Shocking helps manage chloramine levels, but it treats the symptom rather than the cause. And in a heavily used pool, you can find yourself shocking frequently without resolving the underlying issue.
The only complete fix
Chloramines form because chlorine reacts with nitrogen. The only way to eliminate chloramine formation entirely is to replace chlorine with a disinfectant that doesn't produce them.
Bromine disinfects just as effectively as chlorine, but when bromine reacts with nitrogen compounds in pool water, the reaction products are different and far less irritating. There are no chloramines — and no trichloramine — because there is no chlorine in the system for them to form from.
A pool running on bromine chemistry is much more pleasant to be in. The sharp chemical smell that most people associate with swimming pools simply isn't present. The water smells clean because it is clean, without the reactive nitrogen compounds that cause the problem in the first place.