I have two of them, 32g with the wheel asssembly under them. One to mix the new water in and one to siphon the old water into. When I first used them I was getting a film of some sort floating on top of the water, I used a cup to skim the top of the water before putting it into the tank. Now, I don't really know if this was coming out of the can or not, but I think it was, because it dosn't do it anymore. Thses are the cans that Lowes sells.