In my 10 gallon, I have a nice sized pleco, when I got home tonight, he was about 15 feet from the tank. There is an opening about 6"x10" near the back for a cutout for the filter, this is the only way I can think of how he got out, he was hiding in the corner in a pile of damp towels, I quickly put him in the tank. He was pretty dry and hard. He began breathing but didnt move for a while, slowly but surely he began to start using his fins again. I feel like a bad owner now, I gotta get that hole filled up or figure out how he got out I think he's gonna make it. We'll see.....