Twin spot gobies are known to slowly decimate your sand bed fauna then starve to death. Not the best situation for you or the fish IMO. If you are looking for just a fish or something that sifts the sand, I would recommend some snails such as Cerith or Nassisarius (I think that's how it's spelled). If it absolutely must be a fish, then..uh...I will let someone else answer that since I don't really know what a good sand sifting fish is
