Ok I have a 55 gallon with a magnum 350 canister filter ......I am looking to start ove so I'm looking for ideas on what to get.....no cichlids....I'm looking for fish that I can keep in a 55 for a while maybe not life but a couple of years before it out grows it......I had red belly piranhas in the past and loved them but I need something more active/aggresive......any ideas?