Keepers of medium sized to larger cichlids will probably appreciate the phenomenon I'm about to describe: it's amazing how the entire dynamic of a tank full of semi-aggressive cichlids and oddballs can change when you remove one perpetrator or bully fish from the environment. I had recently bought a new cuban cichlid and added it to my 55 gallon CA cichlid tank, and he almost immediately happily inserted himself into the number two position of the tank's dominance hierarchy, essentially throwing the tank into disarray. While my big electric blue Dempsey who has always been the tank boss retained his original position, everyone else in the tank became a lot more fearful, skittish, and generally uneasy from stress. My salvini moved into the cave that was heretofore occupied by my big male electric blue and my small female regular dempseys (who surprisingly tolerated her presence). My firemouth who recently got over a bout of camallanus worms was pushed out of his spot under the driftwood on the left side of the tank, and would just kind of hang out in the open water on the right side of the tank, which he had never done before. My convict was edgier cause the firemouth was impinging on her territory in the back right corner. The catfish who had always hung out in the back left of the tank were now sequestered to the middle and right ends of the tank. Basically this one 3.5 inch fish had taken over 2 square feet of tank space and threw everything into chaos. Today I traded him in at my LFS because he is one of the most aggressive fish I've ever owned. Less than an hour after his removal from the tank everything has gone back to just about normal. The other fish have begun to re-establish their original territories, and most of them are swimming out and about. Has anyone else experienced a similar situation with one of their tanks?