The FROG @ease In-Line SmartChlor Cartridge is used in the In-Line holder built into select hot tub brands along with the FROG @ease In-Line Mineral Cartridge. Together they kill bacteria two ways with up to 75% less chlorine* and create Fresh Mineral Water that’s silky soft with far less odors. It is also the easiest water to maintain because FROG @ease is self-regulating. It knows when more sanitizing power is needed and automatically delivers it. You simply replace the SmartChlor Cartridge when empty and enjoy another 3-4 weeks of worry-free hot tub enjoyment! With FROG @ease, there's no constant monitoring or mixing chemicals. You oxidize only once a month and it's easy on hot tub surfaces with no smelly odors. After 4 months or when draining and refilling the hot tub, it's time for a new FROG @ease In-Line System kit. *Compared to the minimum ANSI recommended chlorine level of 2.0 ppm for a hot tub.