I have two african cichlids in a 55-gallon and one of them is very aggressive towards the other one. Plenty of hiding places are available but one keeps chasing the other out of the hiding places. I'm seriously thinking about adding a couple more to the tank as suggested. However my son has a jack dempsey about the same size as my cichlids. He wants to put something else in that tank now and I thought about putting the jack dempsey in the tank with my cichlids. Can african cichlids be mixed with a jack dempsey? I'm a little leery about doing it. Any suggestions?