yes to limestone, organic dolomitic limestone (not dolomite or quick lime) but DONT
use plaster of paris as that will do very wonky things to the pH and dont use marble.
Ingrid

On Tue, 12 Feb 2008 13:22:47 -0800 (PST), expat wrote:
yes it works, but its a pain after the first one or two
waterchanges.......as you always have to be adjusting the ph with
more of it or you need to do it to the makeup water. I prefer to use
a compound such as calcium carbonate in solid form or some limestone,
that will rasie the ph to the upper side over time but not dissolve
over a short period of time. I have used crushed limestone and
limestone rocks