I know nothing about calcium and ponds, however calcium carbonate rock
(and to a very much lesser extent, calcium sulfate) is something I
have been involved with for many years. Calcium sulfate, or gypsum,
forms some caves, but is most commonly encountered as speleothems
(formations) in limestone, or calcium carbonate,, largely as gypsum
"flowers" or needles. Early on in cave exploration, most cavers used
lamps powered by calcium carbide and water. When calcium carbide
reacts with water, it gives off acetylene, which is burnt, the "spent"
carbide consisting mostly of calcium hydroxide. Caves are formed
largely when carbon dioxide is dissolved in surface water which forms
a weak acid solution which in turn dissolves the limestone, slowly
resulting in a cave. To be sure, there are other contributors to
speleogenesis, but this is a very common cause. I not a chemist, and
not a limestone hydrologist either, but I can't help but feel that
calcium hydroxide and dissolved carbon dioxide play a role in this
also.
--
Galen Hekhuis
I may have mispoken