I saw this question in the tropical discussion, but has not received any replies. I too am interested in flourite for a substrate because of the plants I expect to have. But, since I want a nice school of cories as well, I want sand. So, the question is does the Seachem Flourite (Black Sand) work with cories, or would I be better off going with the gravel type flourite and just placing it in areas where I will plant and leave the open spaces as sand for the cories?