Fishkeeping - help with sick Oranda

I'm almost at my wit's end with my Oranda, Mac! Lets see, he's had ammonia
poisoning, bacteria infection, siphon accident, all within the 3 months I've
had him (a Petsmart fish...) and now I don't know what's going on again. I
gave him 2 hydrogen peroxide dips last week, which seemed to perk him up a
bit. He has stopped flashing, but still just sits in the corner again. His
color is back, but there is still something wrong. Is it possible he did
have flukes and is still recovering?

Right now, I am taking everything out of the tank. He's been in 1
tbsp/gallon salt for 3 weeks. The Melafix has been out for a while now. I
have ordered Quick Cure, and yesterday I also ordered some Medigold food as
well. I want to do one or the other, and which do you suggest I try first?
I am thinking the Medigold.

He doesn't seem to be able to see very well. When I add food, he misses
every time he goes after it. I tried to get him to eat from my hand
instead, but he won't come near me most times. Once, he did try, but
missed. He does find food on the bottom. And, no his eyes don't look
cloudy or anything. He looks fine, other than a bit of shredding of his
fins from the h.p. dip, and his lack of movement, except when looking for
food. I want to put him in my big 90g tank, but not when I don't know what
the problem is. I don't think it's a parasite anymore, and I'm thinking
it's something internal. What do you all think?

BTW, I am doing 30-50% water changes every other day as well, and his water
is fine. Food: he gets one pellet (soaked) in the morning, a pea in the
afternoon, and gel food in the evening. He eats with no problems, when he
can find the food. Another thing I am thinking is that he's actually an
older fish (he's about 3 1/2" long, not including his tail fin). I guess
that's the problem with store-bought fish; you never know anything about
them.

Tammy