I have a new 20 gallon tank that I am cycling now. I am planning on making it an all panda cory tank. I have 5 at present (waiting in another tank until their new private estate is ready). It is the shallow, long type 20 gallon -- 30"x12"x12". What size school would you knowledgeable panda keepers recommend? I want them to have friends, but also to have plenty of "floor space" and not be crowded -- if cories ever feel crowded considering how they way they pile up!