[cypher]

Switching back to the substrate he had before should show if it was an allergy issue or not soon enough.
I know it can be hard to get the best foods where you are so you're probably doing the best you can for him, I don't know the cunipic complete diet though so can't really comment on that, can you get flaxseed (linseed)? If you can I would give him a little pinch of that each day with his food, that should help with skin/fur condition generally.
What about fresh veg, does he have those? If you can work up slowly to daily (if he's not used to them) then give a good variety of fresh, ham safe veg each day, only a small piece of one thing each day but vary it as much as possible.
He's still a good weight so unless he continues to lose more I wouldn't worry, best keep a check on it though.