How big is your tank? How old is it? What fish are in it right now? What type of skimmer, if any? What types of foods (for coral and fish) do you use and how often?
Oh, and don't stir the sand. That would release the nutrients caught in it, and can actually crash the tank. UNLESS, you just stir a little bit of the sand each day. Sand sifting gobies are great for sandbeds, but you need a fairly large tank in order to keep them from starving to death as many won't eat prepared foods.
Did you read the link in my signature? Lots of ideas there... *hint*
