Can you post a picture of your Dempsey? Are you certain that you have a Dempsey? I have heard of a few aggressive JDs but yours seems to be very aggressive for a JD. I'm not saying that your fish isn't a JD, I'm just curious. Also, please do not get a Pacu as suggested earlier. A 4ft tank is not hardly enough for a Pacu. Don't get a male/female pair of convicts either. They will breed and brutalize your JD relentlessly to protect their roaming fry. Take out the JD, move around the deco and maybe add an extra rock or cave, then add a female JD. If not, leave him alone in his tank and watch him grow out as a nice specimen. I wish you the best.
