hey man , i was in your shoes a month ago, i didnt kniow **** about piranhas, only advantage, i had was i have raised south american fish for years,, if uv raised or kept other south american tropical fish, uv got the basics down, i started off with 14, in a 100 gallon, now a month latter i have 9, the rule iv read over and over is 20 gallons per piranha! like joshy said, its just the mater of having to get rid of some fish, to quick, then if u dont get rid of them, u have a stresed tank, witch u dont want, your gonna have eneough trouble cycling your tank, unless uv done it before, man, one beginner to anotha , the best advise i can give u is ''READ'', read as much info on piranhas, as u can find, dont bother with books, between this site and piranhafurry, ull have all the knowledge, ull need, like i said when it comes to cycling the tank, temp, lighting, (i know some say p's like it darker, but i have my lights on a lot and doesnt change there behavior), and sustraight( sand, gravel and decerations, and food) there not that much differnt than any other south american preditory tropical fish,but dont get me twisted , there their own fish , and to be a good ''keeper'' ull have to do a lot of reading, to save you from learning the hard way... good luck homie!