I have a Clown Knife of 7-8" and a Royal Knife of roughly 5" I would like to get a silver, black, or snow arowana as tank mates for the two knives. Is this a good idea? Will they grow together peacefully or will there be problems down the road with fighting between them? They would start out together in a 125-150 gal and eventually move on to a 250-300 gal. Advise on if this is a wise move?