Of a 3-4 comm. made up of a couple of Silvers, a Blacky and a Greeny? I was thinking of adding more Arowanas to the Silver I just got today but I don't know if aggression will be a problem. Here in Singapore many people have Arowana comms of 5 fishes or more but I don't know whether it applies to Silvers/Blacks as well. Will two Silvers fight for sure? What about a 3 piece Silver comm.? Need some expert advice. Thank you!