Is he still breathing heavily? If so, this suggests that a possible pathogen (usually a parasite or worm) is afflicting the fish's gills. I don't think it's anything environmental since you reported that all your other fish seem fine. Fish diseases can take awhile to spread from fish to fish.
@The.SE Are you noticing any of these behavioral symptoms??
Heavy breathing, scratching, flashing, head twitching, yawning, erratic swimming behavior
Swimming into the flow of a water pump/wavemaker/powerhead
I agree (y)
While sometimes Leopard Wrasses will accept frozen mysis, brine, etc. their primary staple is pods. And there's a good chance the fish will starve in just a 30 gallon before it ever transitions to accepting prepared foods.
It reminds me of this: https://www.aces.edu/blog/topics/fish-water/proliferative-gill-disease/
Myxosporean parasites are pretty rare in tropical marine fish, so we don't really worry about them. Is there any way you could take a scrape of the gills to examine under a microscope?
Has the fish been exposed to ammonia or some other toxin which has damaged the gills?
The first thing I would do is give this fish a 30 minute methylene blue bath: Methylene Blue
It might also be worthwhile to place him in a sterile QT with methylene blue at 1/2 dosage (1 ml per 2 gallons of...