I kept CPPDs in a breeding tank and they stayed pretty well to the plants on one side. I've since also heard that in a community setting they are very active and need lateral room (I think it was Happygirl). So, I'm not sure. The Dwarf Rasboras would work. You can also check out Dwarf Hatchets. We have a school of 5 in an 8G semi-column tank and they're a blast.