Model PC-1. Your humidifier stays cleaner, longer. Simply drop in tank for fresh, clean mist; Works in all humidifiers; Keeps cleaning for 3 days; Safe and non-toxic. Concentrated antimicrobial cartridge. Continuous protection against slimy build-up in humidifier. The Protec Cleaning Cartridge features a patented antimicrobial Aquastat, to continually inhibit the growth of odor-causing bacteria and mold in the cartridge as well as help prevent the buildup of slime in your humidifier.