So I figured out why my chromis and goby went midding back in the day. While I was looking at my tank today, I saw some sand which looked like it was being pushed out of a hole i nthe rock. I looked inside the hole and saw a claw or a nose(not to sure) pushing out sand. I also always hear clicking during the night, so I'm thinking I might have a pistol shrimp or a mantis living in that hole!