We are in need of some advice! We have a 500 gal. tank with 400 lbs of live rock. The tank has been established for 2 1/2 years. Every once in a while we have had a fish come up missing. We have also had several of our snails die for no known reason. In the last 3 or 4 weeks we have suddenly been seeing 1 or 2 fish vanish a week. Two days ago I found our very large blonde Naso in the rocks. He had just died, not even time for the arrow crab to begin working on him. I pulled him out and noticed that he has a circle on one side the size of a dime. We have not heard any noises or seen any unknow creatures lurking in the shadows of our tank. Our dealer has just suggested to us that we may be facing a spear mantis shrimp. We have no clue as to what he looks like, where he is living or where we should start looking for him. If you have any suggestions on where and how we should begin our search, please let us know. Thank you so much for any help that you can offer!! 
