On Sun, 24 Sep 2006 11:20:55 +0100, "Davy"
wrote:

I intend to put stones or pebbles in my wildlife pond which won't have any
fish apart from maybe the odd stickleback. My preferred pebbles are
limestone but I have seen a warning against using limestone pebbles because
they can change the ph. Should I take this warning seriously?
thanks, Davy

Seriously? Yes. pH change problem, I don't think so.

Limestone is mostly calcium carbonate and magnesium, for pond keeping
purposes and I use it (ground garden limestone) to maintain KH, (AKA
Total Alkalinity/Carbonate Hardness and probably other names, I can't
recall at the moment.) or the stabilizer for pH. Limestone dissolves
into the water as long as the pH is below 7.8, but once saturated to
that point the limestone stops dissolving. I can't imagine that
being a problem and no it won't cause a crash, but rather stabilize
the pH so it doesn't get into wild swings and crash.

My biggest problem with dissolving garden lime is it's being so slow
in dissolving. After a heavy rain, usually acid, my pH remains
stable, but the KH readings often drop to 1 degree or about 20ppm of
calcium carbonate and 100 is recommended. I wish, but it doesn't
happen for me, still the pH hasn't crashed in more than 10 years of
using limestone to buffer the pH. I sometimes add baking soda, or
sodium bicarbonate, the bicarbonates being the buffer, like calcium
carbonates, or I can clench my teeth and wait until the limestone
finally dissolves enough to bring the KH reading back up to a more
acceptable level, and in my pond that is only about 40ppm, but it
works and the fish thrive. Without it I would have to add sodium
bicarbonate weekly to keep the pH stable.

Regards,

Hal