After recently stocking my tank, I noticed that my bleeding hearts(4) and bosemans rainbows(3) are swimming in the bottom third. The danios, swords and cories are doing their normal thing. I do plan to add a few more rainbows and a pair of bleeding hearts when they become available. Is it a combination of them being new to the tank and not a complete school, the reason they won't swim up higher in the tank? I thought that would be a little more mid level than they seem to be.