I hope that it is not what I think it is, but there are small bubbles forming in the top inch of my sand bed. I have a 16 gallon bow front, with a maximum sand depth of 3 inches in some spots. There are three fish in there, and I do an 8-10 gallon water change once a week. Could this something other than hydrogen sulfide? I also have about 45 pounds of Flordia aqua-cultered live rock.