BCDMH
BCDMH (1-bromo-3-chloro-5,5-dimethylhydantoin) is the most common active ingredient in bromine tablets for hot tubs and spas.
Definition
BCDMH (1-bromo-3-chloro-5,5-dimethylhydantoin) is the most common active ingredient in bromine tablets for hot tubs and spas.
Typical Values: Available bromine: ~54%; Dissolves in about 3–5 days (3-inch tablets)
In Plain Language
BCDMH tablets dissolve slowly to release bromine into spa water. They contain both bromine and chlorine in their molecular structure — the chlorine acts as the oxidiser to activate the bromine. BCDMH is the standard product for bromine floaters and automatic feeders in hot tubs. It is not suitable for outdoor pools where UV would rapidly destroy the bromine.
Why It Matters
Understanding BCDMH helps hot tub owners correctly interpret the product they are using and understand why bromine levels are more stable in indoor environments.
Typical Values
Available bromine: ~54%; Dissolves in about 3–5 days (3-inch tablets)
Last reviewed: 2026-06-01