I've found that filling my humidifier tank w/very warm water and dropping a PoliDent Denture Cleansing table into it and letting it sit for awhile, then given it some good shakes, emptying it and rinsing it w/tap water then a good vinegar and water rinse and setting it to dry keeps my tank sparkling clean and clear. My humidifier tank is the originial that I got and have used almost every night since 26 October 2006. The only nights not used were nights I was at a sleep lab for a new titration and the night I hit a deer carcass on the xpressway and was too tired, lazy and discouraged to haul everything into the motel. I just took my body to the room and fell into bed!