Frog @ease Smartchlor Cartridge 3 Pack is a direct replacement for the Frog @ease Automatic Hot Tub Water Care System. Each SmartChlor cartridge lasts up to 4 weeks depending on hot tub usage (Recyclable when empty). Unlike normal chlorine that is used up when you get in, SmartChlor continues to maintain the same level which is up to 75% less than hot tubs using Dichlor (standard hot tub chlorine). It is self-regulating and goes to work when the hot tub needs sanitizing so there are no frustrating yo-yo chlorine levels. This time-released method is also why less shock is needed to maintain the hot tub. When the SmartChlor Cartridge is depleted the system will flip over as a visual reminder to replace the empty cartridge with a new one.