We normally do not recommend mixing the two products. Unlike sand that filters only on the top 2-3 inches of the bed, Zeobrite is a deep-bed filtering media that utilizes more bed depth for filtering. In addition, the sand and Zeobrite could mix allowing the rough angular particles of Zeobrite to rest against the slick round particles of sand. This could actually create gaps between the partcles where the water flows and reduce the fitering capabilities of the system. It would be permissable to use sand as a support material up to the top of the lower laterals. Since there is no filtering capacity below the laterals, mixing of the sand and Zeobrite would have no effect in this area.