Soilmaster is made from the same high fired clay that Flourite/Eco-Complete is made from, so it a lot of the benefits of the Flourite/Eco, but it's less dense so it isn't as good for holding things down. It is far less expensive than Flourite however, and because it is less dense, it takes more volume to get the same weight. Therefore expect that twenty pounds of Soilmaster will cover more of your tank and at a greater depth than twenty pounds of Flourite.