How do corydoras normally behave?

I have 5. 4 of them are active catfish and swim around a lot and chase each other. But one of them just sits there all day and moves for only like 20 minutes a day. This has been going on for 2 months. he just sits there and hangs out. the weird thing is i've never ever seen any of them eat. I don't know if this helps but they're all albino.