This Humidifier Demineralization Cartridge helps to prevent and reduce the white-dust caused by minerals in hard water. Just drop one humidifier charcoal filter into your humidifier tank and it will start to work. Replace cartridge every 30 to 40 fillings, depending on the water hardness. Includes 10 blue ultrasonic humidifier demineralization cartridges. The filters Compatible with all HoMedics 1-gallon or larger ultrasonic humidifiers. Each demineralization cartridge gets 30-40 full tank uses.