Try soaking nori or seaweed in Selcon or Zoe. If he doesn't take to it right away, try crushing a clove of fresh garlic and soaking the seaweed in the fresh garlic juice also (don't use the bottled garlic or precrushed - it loses its effectiveness). If he will take to it, his color should begin to perk up again within a few weeks.
I use Selcon and have had very good luck with it. Well worth the sticker price.
Good luck!