Thats what I was thinking. Flourite has a really fake look to it, but nothing comes close to its iron content. I've used the screening method on onyx sand to keep the larger grain sizes. It gets rid of all the dust, that I would think would cloud the tank. Could we get a tank pic with the tank filled with water?Brown, in nature, seems more common than black, at least in terms of what ones sees at the bottom of streams, rivers and lakes.