yellow tang sick!

Nori is the dried seeweed sheets used to make Sushi Rolls.  You shoud be able to find it in any grocery store that has an Asian food section.  Alternatively any Asian food store will have it usually in large quantities at very low cost.  You can also find the equivilent at most pet stores, but for a much inflated price over grocery stores.  Though in pet stores defense they also have different variaties.

As long as you tang is eating he will gradually gain weight.  I usually put a quarter sheet of Nori in my tank on an algae clip and let my tangs graze on it until it is gone.  (Actually I use a full sheet, but I have many tangs.  A Quarter sheet is enough for one Yellow Tang.)

Remember you don't want to overfeed you tank so your Tang will have more to eat.  All this does is add food to the tank that will not be eaten and will contribute to reduced water quality.  Simply do your normal feeding, then add a piece of Nori for the Tang to graze on and he should do fine as long as he continues eating.

Good Luck!  I hope both your new friends do well.  Sounds like you already got them through the worst of it.

Also, welcome to the board.

If you give them lettuce you have to blanch it first.  Same goes for spinach.  I've never tried spinach, but it has a lot of vitamins in it.  I usually use Nori because it is more natural to a Tangs environment.  At this point though whatever you can get it to eat is a plus.  Mine also eat any flake food I feed and you could get a flake that is high in Spirulina. (Another type of algea.)  Mine also devour frozen brine shrimp, but they have almost no nutrition.  You might use some to stimulate feeding response though.

Mark also mentioned Garlic Oil.  Not only does it seem to help them fight off Ick, but it stimulates a feeding response as well.  I put a few drops of Kent's Garlic Extreme on a small teaspoon of flake food, let it soak in a few minutes and feed it to the tank.