Bromine works by ionizing contaminants in hot tub water, breaking apart their chemical bonds. It produces a waste product called bromamines, which can reduce the effectiveness of the bromine in your hot tub, but periodically shocking your tub will get rid of it. Plus, you should be shocking your tub, anyway.
Bromine is very reactive, but it’s less reactive than chlorine. That means it kills contaminates more slowly, but this does not make it less effective. In fact, bromine continues to fight bacteria longer than chlorine, so it doesn’t need to be replaced as often. However, if the hot tub is outdoors, the UV light exposure from the sunlight can destroy bromine more quickly than chlorine, so be sure to use a hot tub cover.
The amount of bromine needed varies with the size of the hot tub, but you will most likely need to use more bromine than you would chlorine—unfortunate since bromine is also more expensive. However, since bromine lasts longer than chlorine, it may still be the more cost-effective option.
Both bromine and chlorine are safe for your skin when used as directed, although some people can still have an adverse reaction to either. Bromine tends to be gentler on your skin but takes longer to wash off. It is also better for people with asthma or other respiratory problems.