Alright 'Killer' is an exaggeration but we put a Tail Spot Blenny in the 20G two months ago and the Gramma immediately put the Blennys head in his mouth. Eventually the began to tolerate each other. Tonight we put a firefish in and the Royal Gramma was harassing the new fish to death. The Firefish was curled up in the tiniest corner and looked like he was dead. We have the Gramma in a little mesh holding cage in the 20G. I plan to let the Firefish get better adjusted and then after a week see if the fishes will get along. Will this work?