I have a 55 that I have neons, cardinals, glowlights, bloodfins, greenfires, von rio's, lemons and had black neons and rummynose tetras all together. I also had some serpaes but they got moved to a different tank. Most all the tetras intermingled with no real "game plan" as to where or who they were with. I have no aggressive fish in the tank other than some sailfin mollies that flare at eachother when trying to mate so I guess with no fear, the tetras don't bother to school. My current group of neons and cardinals were all added at the same time. 6 neons and 6 cardinals, they can be found in any number and ratio group at any given time. If they are forced to school (like when I'm cleaning the tank and they get scared), they don't hunt out their own kind, just stick with whoever happens to be close by at the time. Kyle