Caldera Spa FROG Serene Mineral Cartridge provides spa and hot tub owners utilizing the Spa FROG System with an easy way to introduce water softening minerals into their systems in a handy self-contained replaceable cartridge, eliminating the need for time-consuming chemical additives. The Mineral Cartridge softens water as well as making it easy on your skin and eyes to provide a bathing environment that chlorine-based systems cannot match. This product is designed for use with Spa FROG floating or inline systems, making the task of spa maintenance much simpler.