I always thought discus were supposed to be very peaceful fish. I added three new discus to a 30 gallon planted tank containing 1 discus. Whenever I feed the old discus chases the new discus all over the tank and nips at them. I took him out and stuck him in a 10 gallon tank for a week. I put him back in and he continued with his aggressive behavior. So I took him back out for two weeks and put him back in and he is still doing it. When not eating, all is fine. I try placing food in multiple locations in the tank and he'll be eating in one place, see one eat at another location and go attack him. I don't know what else to do. When I isolate him, he won't eat so I'm afraid to isolate him for to long.