Product review (5 stars): Replacing the granules each season is the most cost-effective
4/15/15. I have been using Air-O-Swiss humidifiers for many years and find that replacing the granules each season is the most cost-effective means of maintaining the machine. Of course cleaning the entire unit every month is a best practice since anything that utilized fine water particles is prone to bacteria growth. Cleaning the tank with X-14 bleach and a suitable round brush it wise to remove "scum" buildup in the vent system of my U650 model.  Good machine.