http://www.advancedaquarist.com/issues/feb2003/chem.htm
1. Limewater (aka kalkwasser), used in a reactor or not, and with vinegar or not
2. Calcium carbonate/carbon dioxide reactors (CaCO3/CO2 reactors)
3. Calcium carbonate used without a reactor
4. Calcium acetate
5. One part inorganic salt mixtures
6. Two-part liquid additive systems
7. Water changes