it seems that im the only one who has kept more than 1 black piranha in one tank sucessfuly , i has 3 in a 55 gallon for 3 years,no fighting , or anything,.....as long as you keep them fed their fine ..
Any pictures? You are going to find it hard to gain peoples trust over this with out pictures..
It has always been known facts that if you keep more than one, you always end up with one in a short space of time. I know someone who kept two together for nearly two weeks, but that was after a prolonged attack and bullying of the other.