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Re: silica from substrate

On Thu, 25 Nov 1999, Damon Job wrote:
> I am not sure why sand has been suggested as a substrate in a
> fresh-water fish tank. However, for a planted tank it is common to see
> suggestions of sand-fluorite-gravel from bottom to top. It may be of
> value to point out that some species of algae and diatoms utilize
> silica. hence, by adding sand one might contribute to algification of
> one's tank when trying your best to prevent it with other measures
> (phosphate free fertilizer and buffers).

First, the word "sand" refers to the size of the grains, not their
composition.  Most of the sand we use is predominantly quartz, but it
could be calcite, aragonite or a number of other materials and still be
called sand.

Most of the substrate used in aquariums are composed of silicates. In
addition to quartz sands and many natural gravels, clays, vermiculites,
ceramics, pumice...  They're all mostly silicates.  To avoid silica you
would need to use only pure laterite, calcite, aragonite, peat or
(probably a bad idea) coal.  Oh yeah, and an acrylic tank, as glass is
mostly silica.

Quartz and clays also are normal parts of natural substrates in fresh
water environments.  Silica at around 10 mg/l is a normal component of
fresh water and I've never heard of silica being growth-limiting in
freshwater environments (marine and estuarine environments, maybe).

Roger Miller