I did the flashlihght scan of the tank three nights ago and saw something move rapidly underneath the live rock when the light hit it. It kinda scared me because I thought I knew everything in my tank. Sooo I waited till last night and snuck up on it with the flashlight dimmed and low and behold it was a huge bristleworm sharing the den of a yellow watchman goby. What i saw of it shortly it must be 5 inches long and 3/4 inches wide. I've seen some big ones scuba diving but this big in a tank I have never seen. Should I be concerned? It doesn't seem to be bothering anything. :o