Now don't quote me on this, but I think one of the reasons a calcium or aragonite sugar grain sand is a better choice than a silica or granite based sand is the physical shape of the granules themself. The calcium/aragonite is a softer material, and tends to be softer edged and perhaps rounder. The other stuff may have jagged edges and this can be harder on the microfauna (as well as the glass ... it can scratch the glass quite badly).
I could be wrong but I thought I read something along those lines once.
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-- Tony
My next hobby will be flooding my basement while repeatedly banging my head against a brick wall and tearing up $100 bills. Whee!
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