You said that you are not cycled yet but all your numbers are good on the water paremeters. What does that mean? If you are in the middle of a cycle then chances are you will have some ammonia and/or nitrite in your water. If these levels get too high for ther fish living in this tank then they are put under stress. This will cause some issues with thier behavior as well as some other things. You need to test your water and see where in the cycle you are. Then act accordingly. If the levels are higher then .25 in a cycle then a water change is in order to bring those levels back down to acceptable levels during the cycling process in your tank. It also sounds like there is a territorial issue going on in the tank and since adding more to the school at this time is not an option then I would add more plants, driftwood, and decorations so each one of the fiish can stake out thier territory. I would also recommend moving things around and creating a new aquascape so all of the fish have to re-establish thier territories. This should help the fish that is having a problem with this now. As far as the fish not eating that is probably due to the fact that he is under stress. When the stress is relieved then he will probably start to eat.
Marinemom