Thomas Bartkus wrote:
Okay - I'm confused.

I *do* want to use calcium carbonate based sand because -
It will help keep up the calcium & alkalinity & pH & trace elements as the
sand slowly dissolves into the water. AND it won't scratch the glass like
a silica sand.

I *don't* want to use calcium carbonate based sand because -
Calcium will preciptate out onto the CaCO3 sand and cause the
alkalinity and pH to drop. I will have a heck of a time maintaing calcium
& pH. Better to use a neutral silica or perhaps aragonite sand.

What to believe?
Thomas Bartkus

The answer depends. If you are trying to keep your water levels near
normal sea water, part 1 is very true. It will not though dissolve very
much to suppliment the CA and Alk.

Now if you are trying to run very very high calcium and alk. The CA
will precipatate out of solution. The place it precipatates depends on
many things, one of which is, it forms on other aragonite easier than on
the glass of your tank, but you will find it on your heaters, pumps,
powerheads and any other item that is warmer than the bulk water also.

So for a reef tank, you do want aragonite based sand, but it will not
buffer your water much, but it will be a lot easier on the glass since
it can not scratch glass like silica sand can.

Kim