The Crane Demineralization Filter Cartridge helps reduce white dust, which is a deposit of minerals caused by hard water. For best results replace filter after every 30-40 fillings under normal use or 1-2 months or when the humidifier has not been operated for an extended period of time. To install, simply place filter in water basin. Place full water tank back on the water basin and wait fifteen minutes for the water to pass through the filter before starting the humidifier. Fits Crane Hello Kitty, SpongeBob & Crane Train Cool Mist Humidifier. Demineralization filter cartridge Fits Crane SpongeBob/Hello Kitty Filters water and eliminates dust Extends lifetime of humidifier Lasts for 1-2 months of 30-40 tank fillings