I set up a 75g tetra tank. No plants so far, but plenty of rocks and cover, with ample swimming room. However, one school chills on the left side of the tank, and the other schools to the far right. Pretty much no one stays a long time in the middle, which makes the tank look pretty dumb. How can I spread them out? Can it be I have to much water movement, and they huddle in areas of low circulation?