How deep of sand should there be? We were told 2" deep bottom plus cove sand 6" up side of pool and 4" deep, with an estimate of 5-6 yards for an 18x33 (with compacted leveled ground underneath) The pool directions called for 4-5 yards, but we were given an estimate of 5-6 by gravel company who has done pools. I am ordering in a week and better be sure when its $27 a yard for Masons.