My healthy well established tang is missing?????? Any ideas?

[fishoholic]

Just thought I'd update as it was a week ago that I first noticed my naso missing.

Unfortunately he never showed up and there has been no signs of him in or out of the tank I did have a bit of a cyano break out a few days after I noticed him missing (it's since cleared up) so maybe he died and the cyano was from that Wish I knew what happened