so yesterday i was sitting in the front room and glanced over at the tank, to witness some frenzied attack, all my congo tetras were rounding and fiercely chasing a black phantom as if they were trying to eat it, the poor thing looked terrfied, they all stopped, but i just wondered what the hell was going on....are congos aggressive towards smaller fish...what should i do? 
actually whilst observing them today i noticed if anyone of the smaller fish darts, they all fly around it like its food, does remind me of pirahnas actually. 
