I bought an established 90 gal tank about a month ago. I have live rock, anemone, coral, two clowns, 4 blue chromis, a lawnmower blenny, peppermint shrimp, cleaner shrimp serpent star, and a black spiny urchin. About a week ago I started finding empty hermit shells. At 1st I thought they were just molting but all the shells have holes in them. Could something be killing them?