FROG Serene Floating System uses pre-filled mineral cartridges and bromine cartridges that snap into a reusable floating holder and works in any spa. The FROG SERENE Floating System transforms your spa into the perfect environment for soothing relaxation with up to 50% less bromine needed than standard bromine spas. Cartridges are easily adjusted to meet the sanitizing needs of virtually any size spa. Replace the mineral cartridge every 4 months when you drain and refill your spa. The bromine cartridge will last 2-4 weeks depending on use. BONUS! FREE Frog Test Strips & Frog Jump Start included.