What is the best sand cap over miracle gro that will support the thick carpeting of marsilea minuta? I have leftover Sakrete play sand from home depot, but I am thinking this will be too fine for the rooting of a dense carpet. Would Black Diamond be a better choice? I realize that Amazonia or other aquarium brand substrates will yield the best results for carpeting, but I am looking for something less pricey. Thanks for your help!