It may help explain cory behaviour with this short video of my cory tank. There are 41 cories in this tank, representative of 12 species. Some have several (6 or 7) of the species, some fewer down even to one or two for some species. They are in a post-feeding period of activity in this video, having had their Bug Bites about an hour before, and they are now searching the sand for the left-overs. Several are up on plant leaves, browsing for food particles. But all of this is normal cory behaviour, during a more active part of their day. They go their own ways, but they are together in a good-sized group.