in my 20 gallon tank, I have a blue gourami, 2 adult sunburst platys, 3 baby platys, a pleco and many trumpet snails. I got the gourami from a friend about 4 years ago and he has been doing very well until recently. his pectoral fins have become reddish, on his modified pelvic fins ( the 2 antenna looking thingys), one of them is thinner and spilt in 2, and his gray-blue color has become lighter (almost white). he hangs out a lot by the heater even though the entire tank is the same temp. is he stressed? too many fish in the tank? is it fin rot? is he just getting old? idk how long my friend had him before I got him. I have not released any new fish into the tank, I have not changed anything, not rearranged decorations or plants, in the past 5 months except for a few partial water changes. but I did released my 3 baby sunburst platys back in the tank about 2 weeks ago from their mesh, small box thingy that sits inside the 20 gallon. his behavior has not changed, he eats the same as he usually does. but he looks so bad and it happened so fast!!!! please help me!!!! should I do an entire water change?