The Protec Antimicrobial Cleaning Cartridge features a patented antimicrobial, Aquastat, that continuously works to hinder the growth of bacteria and mold. It also protects against the buildup of slime in the humidifier. The Protec Antimicrobial Cleaning Cartridges work in all humidifiers and contain no harmful chemicals. 1) Easy to use - Simply drop in tank for fresh, clean mist, 2) Each cartridge keeps cleaning for 30 days, 3) Reduces up to 99% of odor causing bacteria, mold & algae growth versus untreated humidified surfaces, 4) Retail pack contains 2 cleaning balls. Blue.