+1 on flukes noe that we know he is more jumpy than anything unlike what you said.

(it's lethargic, not sifting sand, and breathing hard... still eating) cyanide poisoning a fish will eat but he can not digest the food properly. I would use prazi-pro for the 7 day it is also reef safe I have used it in my tank the only thing I noticed was my Nem closed up. May have even shrunk a bit but when treatment ended he opened up right away and is now quite a nit larger. Prazi-pro work great on flukes and freshwater dips also work well. Do not use copper unless you know they have MV as it very hard on a fishes liver and stomach.

Bill