Hot Tub SERUM is a biofilm removal product. Hot Tub Serum can be added to your tub weekly for the removal of biofilm according to the EPA. Hot Tub Serum is an easy-to-use addition to your weekly hot tub care maintenance. It is compatible with all types of sanitizers including @ease, chlorine, bromine, salt, and biguanide. Hot Tub Serum Total Maintenance reaches down deep into the plumbing of the tub to help prevent the recurring buildup of biofilm that affects every spa. When added weekly, Hot Tub Serum will keep the water in your spa crystal clear, soft, and clean.