dont listen to anyone who dosent actually own piranhas is RULE 1
RULE 2 is get your azz to www.piranha-fury.com son!!
man my life changed when I got into these bad boys, but I'l tell you upfront it isnt easy keeping them, theyre not guppies and they have the personalities to prove it. you will need LOTS of filtration and water
P.S the only thing guarantee'd to live with Piranhas is PLANTS and ROCKS