The canopy covers half, and I did have about 60% covered with plastic wrap but it fell off because it was cheap, haha it didn't seem to do much though that I noticed. What does help is putting a damp washcloth over the top, but I don't want the screen to rust. Maybe I should try a better quality plastic wrap. I just moved the tank to my living room a couple weeks ago and that is next to a radiator. So I'm sure that's not helping matters. It is a 18x18x24.