Re: Calcium carbonate

You can buy calcium sulfate at your hardware store as plaster of
paris.  You can mold it into a small lump that can be put into your
tank to dissolve slowly as required.  The addition of CO2 will
promote the formation of CaCO3.  It is not clear that calcium
carbonate is in and of itself useful, tho.  

Dave Gomberg, Experimenta      San Francisco CA USA   gomberg at wcf_com