hi iv just purchased a 120litre tank and im looking 2 get some piranhas (red bellies) how many do you suggest i get for the size of tank i have ? iv purchased the gravel , water conditioner ,filter , heat lamps , thermometer , a syphon , and water test kits is there anything else i will need before i purchase the fish ? i dont think feeding live food is right ,what food is best ? many thanks