They just hide a lot. I love mine, one of my favorites, but I like him because i only see him once in a while. Some people dont like hiders. If you have wood they will just stick to it 24/7. At least mine does, and only comes out when he smells food, sucks up his wafer, and goes back into hiding. But it is a heavy bioload for something you only see 3 times a week. They only grow about 3-4" and would be fine in a 40g. The hoplos are more outgoing.