I have heard that before, but was looking at my tank today while doing some aquascaping and with the canopy up I could see a some filmy stuff on top of the water. I don't think there was anything bad or unusual in the tank (set up with rock, sand, and filter media from my 55), and I keep thinking of all the gunk the skimmer pulls out on my 55 and I do weekly 20% changes on that tank! In the nano I have some shrooms, 2 small hammer corals, some zoas, a small galaxea, a small GSP, 3 hermits and about 4 small snails, and 2 small fish