Picked up a new green terror. Brazy my first one is not allowing it, corners him and everything...hopefully they can work it out otherwise i'll have to take him back, unless someone as an idea.
Try rearranging the tank and and leaving the lights off overnight. You might even want to cover the tank with a blanket. That will cause the fish to re-establish territories and may give the new comer a chance. Good Luck!
putting in a divider will work, i tried a blue acara in my GT tank and the GT ripped that one apart also, i took the acara out for a few days, then added him back when the lights went off, havnt had a problem since, so that could work also