Planted Tank Guru
Join Date: Jan 2010
Location: Contra Costa CA
Forget the sand.
Play sand does not work as well in aquariums as something like Pool Filter Sand, or sand blasting grit, and none of these will work with Safe-T-Sorb or any similar material.
The only way I can keep them apart is to make a retaining wall with expanding foam filler as mortar. Just using rocks without filling the spaces does not work.
I wanted to do a strip of sand in the front of a tank, and Soil Master Select in the back, deeper, behind some rocks. The sand slipped through the rocks and under the SMS. The SMS slipped through a over the rocks and ended up on top of the sand. I can look at the side of the tank and see the layers. Sand down there, a little blended band, then SMS on top.
Skip the sand, use pure STS.