We have a small air stone and Stumpy seems to love standing over it. Think he likes his chin being tickled! We have put lots of rocks over it, and tried to keep it out of their way, but him in particualr always makes a beeline for it, and likes standing right over it. I hope it doesn't cause him any harm. He must like it though if he keeps going back. We have turned the airflow right down though thanks to advice from the pros x