Try treating the food with Epsom Salt to get rid of parasites. Dissolve a tablespoon or two of Epsom Salt into 1 cup of tank water, then put the fish food into the salt mix. let it sit for 10-15 minutes, and then feed the food to your fish (dump the water mix). Did this with Angels, Discus, GT, midevil, and all my africans and never had a problem. Would do this whenever I'd get new fish, and also any time I see long, whitish-clear poo. Do this every feeding for 3 days or so.
As far as that patch you see on his side? It may be hard for us to see in the photo, but to me that looks like the normal whitish stress-bars with a whitish patch in between them. My GT sometimes shows bars and patch, sometimes one or the other, and sometimes solid green sides with a black spot. I think your problem is simply parasites and stress.