You may already know but...
This is one fish to be really, really sure it is eating. The only eat sponges and a select few inverts in the ocean and even when eating in captivity are usually short lived (bad diet). It's very rare for one to live more than 6 months to a year in aquariums. I have heard of a few living several years but this really one fish that should not be collected from the ocean (thousands die for the dozens that make it more than a few years).
Sorry if you already knew all this
Hope you find one that is eating and healthy!