Sodium Bromide is not technically an algaecide, but is used with granular chlorine  as a catalyst to convert the bromides into the potent algae killer, hypobromous acid.  Bromides are usually used not for algae control, but to kill pool algae in out-of-control cases.

Application

Also known as Sedoneural, sodium bromide has been used as a hypnotic, anticonvulsant, and sedative in medicine, widely used as an anticonvulsant and a sedative in the late 19th and early 20th centuries. Its action is due to the bromide ion, and for this reason potassium bromide is equally effective.