Tang off of food?

[reefgirl189]

Can anyone think of a reason that a healthy and vibrant sailfin tang would suddenly go off of food and go into hiding? He's always been the best eater of the group since his introduction a few weeks ago. For the last two days he won't eat. I've tried a variety of 6 different foods to no avail, all of which he's eaten in the past.

The only thing that has changed very recently is the addition of another radion light so the tank is more illuminated now. This hasn't seemed to have affected the other tankmates though as they still eat and act normally. The only thing different with him physically that I can see is that his belly looks empty. His breathing is not any different from the other fish.

Parameters were just tested today at:

Ammonia 0
Nitrite 0
Nitrate >5
Mag 1020
KH 7
Calcium 450
Salinity 1.026
pH 8.2
temp 78