I'm surprised no one has posted this yet, but it was published a few days ago. It looks like activated carbon is the major issue in Head and Lateral Line Erosion. I don't personally keep any surgeonfish, but I know HLLE is a big problem, so I figured I'd pass the word along.
http://www.coralmagazine-us.com/content/activated-carbon-hlle-smoking-gun-found
http://www.coralmagazine-us.com/content/activated-carbon-hlle-smoking-gun-found