Naso Dying?


Reefing newb
I've had a small naso tang for a week now. Every day it has been just fine swimming around making friends with my blue/green chromis. This morning I get up to see it's missing. It was laying behind a rock curved but still alive. Anything at all I can do for it? I'd hate to lose it. I took a pic of it and a short video of it. I moved it to the front so I can keep watch of it and you can see that it's still breathing although it appears it's not normal.

180 gallon tank
Ammonia - 0
Nitrates - 20
Nitrites - 0
PH - 7.8
Temp fluctuates but always around 78-81
1.022 salinity.
I acclimated it in tank over about four hours of putting a little water in, taking some out a couple times per hour just like I have always done. I've never had a problem acclimating a fish. This is a first. I'm about to go get some ethromyacin and plan to dose the tank or move the fish to a smaller tank and dose that.
I wouldn't move him, but if you can dose the tank then do. But if its got copper in it, it will kill any and ll inverts and you will never be able to have any in there again. Try soaking food in garlic first.