Oh my, the fish looks even worse in this photo! The spirobolid worms and spots on the glass make it tough to see what's going on. It isn't velvet, the fish wouldn't still be feeding.
I can't see - does it have spots on its fins, or just the body? If it has spots on the fins and the body, then this is ich. If it just have spots/marks on its body and the fins are clear, then it could be flukes.
I think you need to start a hypo treatment on this fish tonight. That will handle flukes or ich (copper will just handle ich).
Here is some information about hyposalinity:
Hyposalinity Jay Hemdal 2024 This term refers to a long-term bath treatment for marine fishes in which the salt content of the water is lowered and held below the point that certain parasites can survive. The salt level reached, and the time of the treatment are the two variables...
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Jay