Fish all look sickly, yet water seems fine...HELP!

[newreefer_59]

So even though the size of the worm is about 5", he is fine to be left alone?

Ok, so this is what occurred. I had 16 fish. 4 Blue green chromises. several damsels and a percula clown. A Flame angel. A goby. One yellow, Tomini, Sohal and Naso tang that were all about 4" in length. Last night when I arrived back home, I found the Tomini, Naso and Sohal tangs and the Flame Angel all dead and trapped in the live rock and all in the same spot.

It happened Monday as ALL the other fish looked very stressed and sickly. At Wed, they were all looking better, and i found and discarded the dead ones last night. They did not appear attacked though hard to tell, but very decayed. I did another water change, and all 12 remaining fish, crabs and corals look completely fine.

Any thoughts as to what may have happened to the 4 fish that all died in the same spot? under the live rock?