Spa Frog Bromine Cartridge. Spa Frog Bromine Cartridge works with the Mineral Spa Frog for bromine/mineral spa care. Cartridge work in the Frog floating system and in the in-line system. The advantage of using the Frog cartridge system is that it will cut hot tub maintenance time. The Spa water feels softer with the mineral and bromine system because you will be using less bromine. Bromine cartridges last 2-4 weeks depending on the size of the spa, and number of bathers/usage. The Spa Frog comes in-line from the factory on a few spa manufacturers: Emerald, Caldera, Leisure Bay spas, Marquis, Morgan, Watkins Hot Spot, Pacific Hot Tubs, and Saratoga.