A smart teacher of mine told me "Boys will be boys,until a woman is involved","Then all bets are off"........To the victor do the spoils of battle belong.....If you are trying to keep two males together one can and will,fight with the other to prove to the females that he is stronger,If you can find a smaller male,instead of the big one you have that would cut down on agression,but then he could also be attacked,the other fish would be considered collatrell damage,He is only going to pick on the other fish that it knows he can pick on or beat up and get away with it.........