I am 100% postiive that he's eating. That's kinda why stress didn't even really occur to me. He will sometimes spit out the mussels but everything else he devours.
Before I got him he was quarantined with a hyposalinity treatment for over a week. I know this wouldn't kill all parasites but it should have eliminated some of the nastier ones.
Here's a few pics taken just a minute ago:
Yes he does look skinny to me, but I think every fish looks skinny until they are obese TBH.
Since moving the powerhead he's left the wall alone.