Sick Purple Square Anthias

[Nemain]

I went away this past weekend, leaving my fish in the care of a friend. My anthias was hiding when I came home, and I didnt think much of the issue, as he had been eating nothing but cyclopeze for the weekend ( I figured he was just showing his disaproval at the menu - wouldnt be the first time :P)

Yesterday, he stayed in hiding until dinner time, then just sort of swam at mid-level catching something here and there, but certainly not with vigor. He then went straight back into hiding.

I can see no visible signs of illness, butt here is definately soemthing wrong. This fish is such a card usually, very social and a joy to have in my tank. I am very concerned, but have no idea what to do.

Water perameters are fine, all the other inhabitants are super. Just this one fish, with absolutely no outside sign of illness.

Any help is, as usual, much appreciated.

Thank you,

Beth