With him being moved into a new tank on his own, and with transportation etc, it could be down to stress.. How long has he been in this new tank for? What are you normally feeding him on? Maybe try sinking granules?
with the water parameters being so good, and only the one fish in there, i would definately go against 50% daily water changes.. In your position i wouldnt change 50% in a week pal.. If he still flicks and is not eating, i would advise treating your tank with half the stated dose of methylene blue, after that has cleared away, do 20% water change, and maybe add one or two fish to his tank.. Obviously not ones bigger than he is, wouldnt want to spook him.. Try easing his stress levels, maybe adding an anti stress remedy? Hope all ends well. Dean