I'm losing my prized Favia!!! Is it the Filefish or...?

[Myka]

I just got home from work. I am feeding the dogs, and I can hear that my skimmer is overflowing - the glug glug sound of the collection cup lid rattling. It did this yesterday too.

I empty the skimmer cup, and proceed to check out the tank as I always do...and WTF?!?!?!?!?! happened to my prized Favia????? It looks like there is sand sprinkled on it *looks closer* no, it has random bits of flesh missing all over it. It looks like it could be bite marks??!!!

So now I'm eyeing up the Filefish I put in the tank on Saturday. His favourite corner is the same end the Favia is in. I have been watching the Filefish (Bristletail; Acreichthys tomentosus) for almost an hour now though, and I haven't seen him peck at the Favia. He has done a few laps around the tank and pecked at the rocks a few times, but none of the corals.

2 weeks ago I mysteriously lost 1/2 of a Lobophyllia coral very suddenly over a 24 hour period even though the rest of the corals (inc SPS) in my tank look great. This happened in the 24 hours following adding a sump and skimmer to the tank. This was also before the Filefish came to the tank.

Taking that into consideration, and also the fact that my skimmer has overflowed two days in a row has me wondering if it's not something to do with my water, and maybe my Favia is the next to go!! It really does look like bite marks, although the Favia is shrunken up...could just be from the stress of the bites? Maybe the skimmer overflowed because the Favia is putting out chemicals because it is stressed (from bites maybe?) ?? Maybe the skimmer is overflowing because something bad is going on I can't see?

I am just about to do a 10% water change.

Any ideas???