Pool smells strongly of chlorine: it's actually running low
- Active chlorine barely smells at all: what smells strong is chloramines (chlorine "spent" on sweat and cosmetics).
- Strong smell + stinging eyes = high combined chlorine = a shortage of active chlorine.
- The remedy is counter-intuitive: you add chlorine (a shock chlorination) to destroy the chloramines.
- The app measures the free/total chlorine gap and calculates the treatment for your pool.
It’s pool misconception number one: “it smells of chlorine, there must be too much”. The reality is the opposite. Active chlorine, the kind that sanitises, barely smells at all. What stings your nose is chloramines: “spent” chlorine, combined with swimmers’ sweat, urine and cosmetics. A strong smell therefore signals that the chlorine is burning itself out in those combinations — and that active chlorine is running low. The remedy, counter-intuitively: add chlorine, in one shock chlorination that destroys the chloramines. The dose depends on your combined chlorine level and your volume: the CliniPool app calculates it from your test.
The chemistry in two sentences
When chlorine meets what swimmers bring in (sweat, cosmetics, urine — all rich in nitrogen), it forms chloramines: compounds that barely sanitise any more but smell very strong and irritate eyes and skin. On a strip or a test, it shows up in the gap between total chlorine and free chlorine: the difference is combined chlorine — the chloramines.
The diagnosis in 30 seconds
Test your water measuring free AND total chlorine. Three possible readings: free fine and total close to it → all good, the smell comes from somewhere else; free low and total clearly above → chloramines, that’s our case; both at zero → there’s simply no sanitiser left.
The treatment: burning off the chloramines
The method is called breakpoint chlorination: raising the free chlorine high enough, in one go, to completely oxidise the chloramines. That’s the whole point of the dosing: too little, and you create new chloramines instead of destroying them — the classic mistake of repeated small top-ups “because it smells”. The right dose depends on your measured combined chlorine and your volume; the app calculates it and guides you, swimming break included.
During the treatment: continuous filtration, and if the pool is indoors or the hot tub covered, ventilate — chloramines leave through the air too.
And afterwards
Once the smell is gone, prevention is simple: keep the free chlorine stable (low drifts are the chloramine factory), encourage the shower before the swim, and oxidise after busy days. The app watches the free/total gap at every test and warns you when the combined creeps back up — before your nose has to.
Frequently asked questions
Why does my pool smell of chlorine when I've just added some?
If the smell persists, the added chlorine is immediately combining with the organic load (sweat, cosmetics) and producing smelly chloramines. You need a shock chlorination to "burn off" that combined chlorine — not little top-ups.
Is the chlorine smell dangerous?
Chloramines irritate the eyes, skin and airways, especially in indoor pools or covered hot tubs. A strong, persistent smell is reason enough to treat and ventilate.
How do I know if I have chloramines?
It's the difference between total and free chlorine: if the total clearly exceeds the free, the gap is combined chlorine (chloramines). A test that measures both is all you need.