Neon tetra problem !?

This can happen sometimes if the same small school of fish are in the same area for a long period of time. This exact situation actually happened to me not that long ago. The first thing I did was switch around the tank and buy a few different decorations. This will help break up any territories that the big ones hae claimed and make it all new to everyone. Then, I went out and bought three new small fish. I did this for two reasons: so that the school was up to the healthy numbers and so the new fish had some others to hang with that were new too. After all of this everyone seemed to get along fine and pal around like they used to. I hope this helps and good luck to you and your fish. :)