Ok, I got a diamond back goby last week, and it was very sluggish and just stayed in the same spot on the sand...and not very active. So I thought it was just acclimating to the tank... Two days later, I cannot find the fish anywhere in my tank. My tank is completely sealed on the top except a hole (quarter size). I only take the top off when I feed at night. I looked everywhere...and he just vanished into thin air. Now my only fish is a six-line wrasse in my tank...and he seems very happy. Do DB gobies dig into the sand and hide, geez, I've combed every inch of that tank...and my tank isn't that big. I'm fairly certain that there isn't any predators either. Any ideas on how a goby can just disappear? :-/ I will continue to search for it...it's just very strange to not find a trace of it.