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The chemical formula for bromium is Br2. It is a reddish-brown liquid at ordinary pressure and temperature. It is volatile and emits suffocating, irritating and toxic vapors. Its chemical behavior in water is similar to that of chlorine but different in that molecular bromium and hypobromous acid subsist at high pH. Given the oxidation-reduction potentials of the different species, the oxidising power of bromium compared to that of chlorine is weaker in an acid medium, comparable in a neutral medium and better in an alkaline medium. In addition, bromamines are more unstable than inorganic chloramines.

The antiseptic and algaecide properties of bromium are used for the disinfection of swimming pool water. Bromium is particularly well suited to situations where the irritant nature and the smell of chlorine can be offensive such as in whirlpool tubs. Bromium is added to water as pellets containing 70% of active bromium, dispensed using a brominator mounted on a by-pass loop by the recycling circuit. The amount used is approximately 1 g · m–3.