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Bromine in tablet form contains almost half chlorine. Specifically, it is "Tri-Chlor," and that is the worst thing you can do to a spa. I use it in open spas or pools ONLY.
I have found that it doesn't matter which bromine tablet you use: if it is in tablet form, it will damage your headrests, cover, and maybe even pump seals. The exception is Brilliance, which contains no chlorine, but it IS NOT in tablet form.