My GSM clown is the only fish in one of my 10g tanks since I bought him almost 2 years ago. He had a mate, but she didn't survive transport to the store. He has displayed what seems like an instinctual behavior since I brought him home, clearing the sand all the way down to the glass. "He" is now a "she" after all this time, and even though she is still the only fish in the tank, she still displays this behavior. HTH.