What's up with my Acan?

Quite possibly. It's definitely bacterial, as it's spreading around. Only to acans so far, though.

I think I found the cause of my issues. I went downstairs and looked at the tank just now, and there was a porcelain crab picking at one of the surviving acans, and another picking at my duncan. These stupid crabs are damaging the corals, which is letting the infection spread.

So, now that I have yet another reason to despise the hitchhiker crabs, what eats crabs but not coral? I don't care about my duster, my shrimp, or anything other than my fish and corals at this point. These things need to die, now.

 

Some of the non reef safe wrasses eat clams/shrimp/crabs/snails...

Hence being not reef safe. lol.