I have cories, too, in a 50/50 fluorite/pea gravel mix and they're fine. I
mixed in the pea gravel (cheap from Home Depot) because I simply could not
afford to go with a pure fluorite substrate in my big tank (55 gal).

If you want a black substrate, what about Onyx? This is reputedly as good as
Fluorite, but it's black, which I think looks really good. I have a ten gallon
tank with a pure Onyx substrate and am very happy with the results so far. The
texture is finer than Fluorite, too.

HTH


Erica
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