Sick Anthias

[SuncrestReef]

I've had two anthias in my 88 gallon display tank for over 6 months and they've been healthy and active. Yesterday, the larger anthias began acting oddly, swimming vertically and twitching side to side. Today, he's just laying nearly motionless on the sand at the back of the tank. Still breathing normally, and no visible spots or other symptoms. During feeding he did eat, but just swimming very slowly and erratically. All my other fish including the smaller anthias seem fine.

All water parameters are normal, and I test frequently.

Any ideas what would cause this, and any suggestions for treatment?

Video from yesterday:

Photo today:

[Vance164]

I just had this happen to a clown and blue spot wrasse not sure what caused it. unfortunately neither made it. 

[Snappy]

My anthias have one of the 4 behaving oddly the last few weeks. One seems to permanently hide in the cave. He still eats and breathes fine. Takes a real bit of movement to stay on the side of the cave wall in the fashion it does. I think mine is a runner up male hiding from alpha male. Not positive. Yours looks similar to mine, but also a little different. Hope it make it through. 

[InLikeFlynn]

Not sure if you carbon dose, but I got this lethargic swimming from the two most active fish in my tank when I started dosing Red Sea NoPox.  I used their recommended dose, but I think it made the aerobic bacteria so active it drove down the O2 for the fish.  They did not have labored breathing that I could tell and I never got the cloudiness of a bacterial bloom, but they did swim that way and sometimes just laid there on the sand/rock.   I reduced the dose, and increased surface agitation for more gas exchange and they returned to normal the next day.  Might be something to look at if you do.

Good luck, I hope you are able to save your fish.