PureGuardian GGHS15 Aquastick Antimicrobial Humidifier Treatment, Pure Guardian humidifiers and All Brands, Reduces Mold and Odor causing bacteria in Ultrasonic and Evaporative humidifier water tanks The AquaStick humidifier water cartridge helps reduce the growth of mold and odor causing bacteria in the water of a humidifier tank. It can be used in both evaporative and ultrasonic humidifiers. One Aquastick can be used in humidifiers with a tank that is up to one gallon in size. For humidifiers with a capacity of one to two gallons, use two AquaSticks For best results, it is recommended to clean your humidifier tank according to the manufacturer's instructions, before using the AquaStick and to use clean, fresh water. Needs to be replaced every 90 Days depending on use and environmental factors. Can be used with most brands and types of humidifiers.