The SPA FROG®  In-Line System enhances a standard hot tub up to 600 gallons with its patented delivery of minerals and a low dose of bromine. This hot tub Fresh Mineral Water®  system eliminates the need for daily maintenance & chlorination, improves spa water quality and removes the unmistakable smell of chlorine, all the while reducing bromine use and enhancing your hot tub water quality. Simply snap the pre-filled mineral & bromine cartridges into the holder, sit back, relax and enjoy your hot tub.