The gravel from homer depot was a 50lb bag of their "pea gravel". The grain is a little bigger than you typically see in aquariums, but it worked. I am sure your natural gravel will work fine. Others will warn you about your poly eating the gravel. I can neither confirm nor deny it. I figure the bigger grains that I got will lessen the possibility of a mistaken grain eaten, and the small grains of sand will pass easy. So... YMMV.