I would feed him 4 pellets a day (2 in the morning and 2 at night), bump up the heat to about 80F degrees, and cut down the water changes. I feel like you can get away with a 50% and then a 100% every week. I'm sure he gets a bit stressed with all the water changes, lack of food, and cold. Once you fix all of this I'm sure he will regain some color and start to regrow fins. He honestly looks fine to me.