FROG 01-14-3883 Serene Floating System keeps your hot tub clean while eliminating the work and the guesswork. Instead of spooning in bromine daily, you simply replace a pre-filled cartridge about once a month. FROG Serene works by killing bacteria in two ways 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.