OK.. how bout PH? if this is an adult naso... your tank is too small IMO, but besides that, try picking up some ocean nutrition formula 1 or dried algae sheets. I would also consider soaking your food to help not only entice.. but to keep him as healthy as possible in that size tank.. .not trying to flame you, just tryin to help.. I use Zoe, Zoecon, Selcon, and Xtreme Garlic for ALL my foods.. and my fish love it!