I've noticed that. At night they are pretty stationary, but twice I have found him just floating around. I can push him to the side and he grabs on and off to the races he goes. Not really sure lol.If the overflows are in the dark, they don't like dark. And at night they don't seem to move much. But in a reef, they still find their way in. The larger ones seem to know better and I didn't lose any adults that way.