FROG Serene® 01-14-3856 Cartridge Kit - The FROG Serene® Cartridge Kit includes 1 mineral cartridge and 3 bromine cartridges. FROG Serene® keeps your hot tub clean while eliminating the work and the guesswork. FROG Serene® works by killing bacteria in two ways with sanitizing minerals and a very low level of bromine.