You might need to assess the quantity and quality of the food supply available in the tank for the pb to graze on throughout the day. If there is not enough or if it's not a quality green algae (if there is enough and he doesn't eat it, it's not a quality algae), then you should probably make the nori sheets available all day long.
The best flake food to feed is spirulina for tangs, and, there is 95% spirulina flake available from Jehmco that is great. (most spirulina flake is actually only about 45% spirulina)
I am assuming the problem is not due to parasites as you never mentioned any signs of flashing on the rocks, or any visible parasite.
If the fish gets run down though, parasites can get a real foothold and then you will be battling on two fronts.
If you feel the tang is getting worse you may also consider putting it in a hospital tank and treating it with vitamin C and B complex vitamins, if nothing else shows to suggest a specific treatment. |