08-21-2007, 08:38 PM
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I must agree with F4A. The little bit of light reflected from the gravel isn't going to do anything for your plants, and it will probably have a negative effect on your fish. Plants aren't ignorant of the sun's position; it's above them, not below. Thus, most of the chlorophyll that any plant's cells produce is going to be on the top of the leafy area.
A white (or light) substrate can actually be harmful to your fish. They feel less secure with a lighter substrate than a darker one, stressing them out, and making them more susceptible to disease. I also hold no doubts that, in the long term, it could be damaging to their eyes, just as snow is damaging to our own.