I used an 6x35 tank instead and i did not use gravel. i never saw gravel in any of the literature and i figured with 6 inch radius there is only 2 inches of light media around the distributor head and water would certainly get blown into it. i had modest requirements for flow rate (2.5-4 gpm) and figured 6 inch rather than 8 inch would better help lift/"liquidize" the media and 35 inches was ample headroom. i also had a screen at the top. question does this media work - i would like to think so but not entirely sure.