what Bill says... but I will tell you that IF the pH of your water out of the tap is
below pH 7.0 or so that conch shell will dissolve rather rapidly. Ingrid

On Mon, 18 Feb 2008 14:12:29 -0500, "Bill Stock" wrote:
Shells can also be a good thing, as long as they're free of contaminants.
They act to buffer (add KH) the water, which keeps the PH from crashing as
your water gets dirtier with age. I keep Aragonite (crushed coral) in my
Goldfish filters to keep the PH up. With weekly water changes the PH stays
somewhere around 7.6. It's unlikely that your shell would have the same
surface area as crushed corals, so it would have much less impact on the PH.
I have quite a bit of Limestone in the pond, which keeps the PH around 8.6
and the fish don't seem to mind.