if you get them from the same litter and keep them fed they will be fine , i live in D.C and the pet stores always have a school of black piranhas.plus a school of gold piranhas.and they even have red bellies mixed with caribe piranhas .you have to keep the temp,atleast 75 to calm them down. And always keep a huge rock or drift wood ind the middle to seperate sections. The light has to be dem so that they are comfertable. A piranha can be in a tank for years and still be uncomfertable. And leave some fake plants drifting at the top .Now the problem will be if you try to put a piranha in the tank that is not from that litter they will be crushed.And you have to have a deesent tank size ofcourse you cant stuff 10 in a tank .I had 3 in a 55 gallon for 3 years .My dad kept 4 in a 120 gallon .and my cousin has 3 in a 90 gallon
.................................................................................................ROOKIES!
.................................................................................................ROOKIES!