eh how thin ? and what grade sand are u looking at ? if its like 1 or 2 cm of grade 2 or smaller then dont bother... the current in your tank will move the sand forming craters where the glass bottom can be seen, not very nice , unless its more than 1 inch IMO. i am using grade zero around 1.5 inches. the depth of my sand bed isnt very even because of the currents in my tank, but bare glass bottoms arent seen.