"Wayne Sallee" wrote in message ...
I actualy add potasium silicate to my reef tank, to
encorage diatom algae. But no, silica sand does not
disolve well in in the aquarium, and nether does the
silica glass that holds the water in.

It does not dissolve well - this is true...
But in chemistry there is not such thing
as unsoluble substances - water is so great
that *some* amount will always dissolve in it.
For some substances it will be much, like NaCl
or sugar. For some others, like CaCO3 it will
be only 400mg/l and then it stops, but still
some amount will find the way to the water.

Compare data for silicon dioxide (quarz)
with data for calcium carbonate CaCO3.
http://www.ilo.org/public/english/pr...8/icsc0808.htm
http://www.ilo.org/public/english/pr...1/icsc1193.htm
They both are listed as "insoluble", but we aquarists
know better than CaCO3 is in fact soluble in water and
we can get concentrations of calcium on the level of
450mg/l from CaCO3 without any big difficulties...

Also - there is silica available in sea water,
so it must come from somewhere - I would be
interested in knowing what is the source of
soluble silica in the sea water. Diatoms are
able to get it somehow for their own usage...

Interesting subject - I wish I knew more about chemistry :-)