For a few of my aquascapes and biotopes I hope to create in the future I want a very fine white powdery sand. It's meant to be a sort of Rio Negro type sand. The ADA catologue has 'Rio Negro Sand' in the substrate section and this is exactly what I'm looking for. Although Aqua essentials don't stock it. I'm really not looking for the silica/silver/play sand types - a lot finer and lighter. I know this might be a long shot, but does anyone know where I can buy such sand?