FROG Serene Floating Cartridge System keeps your hot tub clean while eliminating the work and the guesswork. Instead of spooning in chlorine daily, you simply replace a pre-filled cartridge about once a month. FROG Serene works by double-teaming bacteria with sanitizing minerals and a very low level of bromine. The resulting Fresh Mineral Water has a completely different quality that provides the serene feeling you’re looking for.