have you read all of the info on piranhas in the killfish forum. there is quite a bit of really important info in there. i highly recommend thoroughly reading those threads that are stickied. I speak from personal experience as i have owned rbp for some time now. They arent the type of fish many people expect them to be, if all you know of them is youtube videos. They are typically misunderstood fish, and can be "skittish" to own if not kept in the right conditions. Please think the decision through with an open mind to the idea of possible going with other fish. they arent right for most people. i have seen a lot of people i know personally, buy them and get bored quickly. they then sell them off, blaming the fish for being the only way they know how to be...
Would these be your first fish?
Kyle