FROG Serene Replacement Bromine Cartridges for use with Hot Tub FROG Serene Floating Sanitizing System - Prefilled for Quick & Easy Hot Tub Maintenance - 4 PackBrand: FROG Color: Yellow Features: Cartridges for Hot Tub Maintenance: FROG Serene Bromine Replacement Cartridges are designed for the FROG Serene Floating System Enhanced Sanitation with Bromine Cartridges: These cartridges sanitize the water along with FROG Sanitizing Minerals Long Lasting Cartridge Use: Each FROG Serene Bromine Cartridge lasts 2 to 4 weeks, and when used with FROG Minerals, reduces bromine use by up to 50%*; once the cartridges