The FROG Serene Bromine system is an inline cartridge or floating cartridge sanitizing system that is made to keep your water fresher than ever. The yellow cartridge contains bromine and the blue cartridge contains minerals that work together for optimal sanitization. This self-maintaining system makes taking care of your water effortless, with the bromine cartridge having to be replaced every 2-4 weeks (depending on the size of the spa and how much it's being used) and the mineral cartridge being replaced with every drain, clean, and refill (every 3-4 months).

These are singular FROG Serene Mineral Cartridges.