A well-treated pool, with chlorine and pH in range, barely smells at all. If you notice that sharp smell everyone recognizes as "pool smell," what you're smelling isn't the chlorine that's disinfecting, it's chloramines, and their presence means the water needs attention, not that it's especially clean.
That smell isn’t chlorine: it’s chloramines
What chloramines are
When chlorine comes into contact with organic matter in the water, sweat, sunscreen, skin residue, urine, it reacts with it and turns into chloramines. It's literally "spent" chlorine: it has already carried out its disinfecting job on that dirt and is no longer available to keep doing so. The more people who swim without showering first, the more organic matter there is in the water and the more chloramines are generated.
In the Comunidad de Madrid, the regulatory limit for combined chlorine is 0.6 ppm maximum, above that value, besides the smell, the water is considered to no longer meet the required sanitary criteria.
Why the strong smell is a bad sign, not a good one
This is the industry's most common misunderstanding: many people think "it smells strongly of chlorine, so there must be a lot of chlorine." The reality is the opposite. The chlorine that actually disinfects (free chlorine) barely smells at all. What smells strong is combined chlorine in the form of chloramines, chlorine that's no longer working. An intense smell usually means little free chlorine remains available relative to the accumulated dirt, exactly the opposite of a well-protected pool.
Other signs that it's chloramines, not a lack of cleaning
- Red or irritated eyes when getting out of the water, even if the chlorine test looks correct.
- A feeling of dry or itchy skin after swimming.
- The smell is more noticeable in indoor or poorly ventilated pools, where chloramines build up in the air.
- The smell gets worse after days with heavy bather traffic.
How to fix it
Adding "a bit more" regular chlorine doesn't solve the problem, a real shock chlorination treatment is needed, one that raises free chlorine well above the chloramines present until those compounds are broken down completely (what the industry calls reaching "breakpoint"). Once that balance is broken, the smell disappears almost at once, not gradually.
Frequently asked questions
If it smells strongly of chlorine, does that mean the pool is very clean?
No, it's exactly the opposite. A well-chlorinated, balanced pool barely smells at all. The strong smell comes from chloramines, which indicate that chlorine is being used up neutralizing dirt instead of being available to disinfect.
How do you get rid of the chloramine smell?
With a shock chlorination treatment that raises free chlorine well above the chloramines present. Adding a bit more regular chlorine doesn't solve the problem.
Are chloramines dangerous?
They irritate the eyes, skin and airways, especially in poorly ventilated spaces. They're not cause for alarm, but they are a clear sign that the water needs treatment.