Naso tang not eating

[Recife]

My naso tang stopped eating in the last few days. He swims by the food and eats a flake here and there, but definitely not enough for his size (5+ in) and in comparison to the voracious eater he used to be.
All the other fish are behaving normally and I don't recognize any sign of disease in him. The only change in the tank recently was that I added a Moorish Idol (I know...) a couple of weeks ago, who the naso chases after sometimes.
The naso is clearly starting to lose weight and look weaker.
Do you have any idea as to what might be causing that? I haven't changed the food and the water parameters haven't changed.
He's refusing Prime reef flake, seaweed salad, frozen mysis and brine shrimp, all of which he used to eat like crazy before.
Any suggestions?

He's my favorite fish and I don't want to lose him. Please help...

 

[ronj]

you could try using garlic to entice him to eat again....a naso tang needs brown seaweed in its' diet preferably with vitamins and hufa's added to it..(aka..Kent Zoe and Zoecon).....i wouldn't rely on flake food at all for this species....does its poop look stringy or white????