With a fish that size, I'd worry about the quantity of food more than the actual type. Ideally a baby fish like that can graze constantly throughout the day, so try doing small feedings up to 6 or 8 times. If you can put an auto feeder in place it can take some of that pressure off of you for feeding.
That being said, I like to offer all my tangs a good variety. My best product recommendation is probably the shredded algae that Two Little Fishies puts out. It rehydrates really nicely if you mix it in some water and it's good to mix in with your thawed frozen foods. I like that much better than the flat seaweed or especially food grade Nori.
Also, Ctenochaetus sp. tangs tend to rasp algae off of various surfaces, so if you pick a panel and decide not to algae wipe that it as often it may allow him to find more algae to graze on between feedings. When I forget to algae wipe for a couple of days, I notice little "kiss" marks on the glass from my yellow-eye tang (also a Ctenochaetus). Hope he does well, good luck!
