FROG @Ease Replacement SmartChlor Cartridge for use with Hot Tub FROG @Ease Floating System Hot Tub Sanitizer System Supports Less Chlorine Use 3 Pack Tilcare Includes convenient hang tags to Northside General Products Includes convenient hang tags to alert others when they can safely re enter treated area It's working method: a high sensitivity photoelectric sensor to detect smoke and high stability electrochemical co sensor to detect carbon monoxide Self Regulating Water Treatment: SmartChlor Cartridges require no maintenance or monitoring each cartridge lasts 3 to 4 weeks depending on the size of your tub and how often it is used