Someone recently gave my son a beatiful goby ( do not know what kind) he is black with a pretty yellow pattern. He is about 6 inches. He has a hiding cave under the rocks but he moves mouthfulls of sand every night, and my sand is very fine so in the morning the tank is cloudy and sandy, and all over the rocks and corals!! Is it possible to get a different type sand or is this a lost cause.. Mt son just loves this goby.