Spa Frog Refill Kit contains 4 pre-filled mineral and bromine cartridges that snap into a reusable floating holder and works in any spa. The SPA FROG® Floating System transforms any spa into the perfect environment for soothing relaxation with up to 50%* less bromine than standard a 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. Contains 3 Bromine and 1 Mineral Cartridge per kit.