Are 5-2-3" discus normally aggressive enough to kill otocinclus, guppy, and cory? They are attacking each other, flaring gills. They have killed all of my little fish. Except a little oto, a couple guppies, and 2 corys. Keep in mind i still have lots of other 'bigger' fish in there like rainbows, hatchets, big tetras, and so forth. I had no idea discus would be so mean? Their are pecking CONSTANTLY at everybody in the tank! Pecking is mainly what they do, none of the fish are bitesize IMO but they just compulsively nip the heck out of everybody! I just caught them nip my bristelnose 3 times around the bristles! They almost killed one of the last corys when he started swimming out in the open again! Their so mean!