We get asked this question all the time: I've got a hot tub. What's the difference between chlorine and bromine in my spa?
There are a couple differences. Chemically, they are closely related, being next to each other on the periodic table. However, in hot water they react very differently.
When you first add a chemical to your hot tub, you are creating a residual, or trying to. Chlorine has a very short life in hot water, so when you add it, it'll go in, kill germs and bacteria, and be gone pretty soon – as in within hours. Some people like this, some do not. I'm drawn away from it because I do not want to have to worry as much about my hot tub maintenance. With chlorine, you may have to add some every day, depending on how often you use your tub. Once the heat and bacteria affect it, it is gone from your water.
Bromine, on the other hand, acts differently. Bromine is like Sleeping Beauty. It is very stable in hot water, and able to hold a residual much better. This means that despite the price on a bottle of bromine is higher than chlorine, you will not use nearly as much. Plus, you can “wake up” bromine. Its a very hard worker – when you put bromine in the water, it'll work for many hours, killing germs and bacteria. When it's all used up, it lies dormant, sleeping, until you add a little bit of non-chlorine shock to wake it up. That shock, in this case, is like Prince Charming's kiss. Bromine will wake back up and get back to work.
Bromine enters water —> kills germ, combines with those particles —> bromine “sleeps” —> add a couple tablespoons non-chlorine shock once a week —> the bromine that you ORIGINALLY put in the water wakes back up and starts cleaning house again.
Chlorine has a lower initial cost, but will require more attention from you, and you'll need to add it fairly often. Bromine is less maintenance and you'll use less of it, lowering your cost over time.
If I were choosing which one I would want to use for my own hot tub, I would choose bromine.
If you hear a friend of yours talking about how their hot tub never sees to hold its sanitizer, or that they have to work hard to keep their chemicals correct, ask them what they are using! You could save them a lot of trouble!