I had a Golden Gourami in a 10 gal tank by himself for about 7 moths then I upgraded to a 30 gal and put him in there with on more golden gourami and 7 red fin tetras. At first everything was all rainbows and sunshine as everyone was getting along...that changed about a week ago. Now the first gourami I had (biggest fish in the tank) is bullying everyone. He stays on one side of the tank and if anybody even looks at him he charges. What can I do to change this behavior or is it a lost cause?