The Spa Frog lets you reduce chemical usage up to 50%, with bromine and chlorine levels as low as 1 ppm. Unlike Nature 2, the patented mineral formula in Spa Frog is safe to use with bromine. This floating dispense is for use in any spa or hot tub. The Spa Frog system keeps the water in your spa clear and sparkling. The floating system includes one mineral and one bromine cartridge. The cartridges are pre-filled and snap into the reusable floater, making spa care easy.