"George Burnt" writes:

If using tap water for a reef is a sin because it might contain silicates,
why is it ok to use silica based sand? Or I am I compaing apples to oranges
here.

The solubility of SiO2 (glass and silica sand) is incredibly low, to
the point that you will never detect the silica that dissolves from
sand in an aquarium on any test kit you can easily buy.

Actually, it's okay to dose silica to a tank (I do it to maintain
silica at 1ppm). Diatoms are an important food source and serve
to naturally remove nutrients from the water that can then be
skimmed or consumed by filter feeders, etc.

The problem comes when the water change water is at 20ppm silica and
your tank goes suddenly from .05ppm to 5ppm. Those are the conditions
under which you get a bloom. I get occasional "blushes" where some
patches of the sand get a reddish darkening, but those disappear within
a day or less in my tank (good live sand crew).

Here's a pretty good article on the subject (including your sand
question): http://www.advancedaquarist.com/issu...03/feature.htm

Regards,
Ross

-- Ross Bagley http://rossbagley.com/rba
"Security is mostly a superstition. It does not exist in nature...
Life is either a daring adventure or nothing." -- Helen Keller