By The Zagosa Team. Published .
Reviewed or updated .
Chlorine and bromine kill the same bugs. What separates them is smell, skin sensitivity, the temperature you run at, and how often you can get to the tub to test. There is no outright winner, but for most UK owners bromine comes out ahead on three of those four points.
How each one behaves
Chlorine acts fast and fades fast. It oxidises organic matter quickly then dissipates, especially in warm water, so you tend to dose little and often.
Bromine works in a slower, steadier way. It copes with higher temperatures (it is the same active species at 30C as at 40C, whereas chlorine loses effectiveness above roughly 35C) and usually lives in floating feeders or cartridges that release it gradually.
Smell, skin and stability
Bromine smells less. The compounds it leaves behind after dealing with organics are less volatile than the chloramines chlorine throws off, which is why bromine tubs feel gentler on the eyes.
For sensitive skin, bromine is usually kinder. People with eczema or dermatitis often switch to bromine and stop reacting.
Bromine holds up better at hot tub temperatures, and that stability is the biggest single reason most UK specialists recommend it for a domestic tub.
When chlorine makes more sense
If you only soak at weekends and want to dose-and-forget through the week, slow-dissolving chlorine tablets in an in-line feeder do the job well.
If you also run a pool and want to share chemicals across both, chlorine keeps life simpler.
If cost outweighs convenience, chlorine granules are noticeably cheaper per kilo than bromine tablets at retail.
Common questions
Can I switch between them without draining?
Not cleanly. The two reseed each other's spent cells in the water and you spend weeks chasing readings. Make the switch at a refill.
Which is easier to test?
They need different test strips and different drops. Both are straightforward, but you must use the correct test for the sanitiser you are on, or the readings mean nothing.