I have 2 Percs in a 120 gal with several other species. They have been in the tank for about 4 months now and had spent those 4 months on one end of the tank exclusively, no more than 5 inches from each other. As of about a week ago, one has ventured out to the other side of the tank to hang out, leaving the other back in the original spot. My water quality has remained excellent through out the months and there have been no other changes to the environment. Any thoughts?