Dosing Kalkwasser as a method of supplementing Calcium was supposedly first used by Peter Wilkens of the Berlin Aquarium Society. Kalkwasser is just the German word for Limewater. Lime is the common name for Calcium Hydroxide. So Kalk is just another name for Calcium Hydroxide, which has chemical formula Ca(OH)2.
No matter how you add Calcium to your tank, you are really just adding the Calcium ion, Ca++, which is produced when the Ca(OH)2 breaks apart in the water into 1 (Ca++) ion and 2 (OH-) ions.
There are many ways to add Ca++ to your tank, the only difference being what the other part of the chemical compound is that's left over when the compound breaks up.
If you used Calcium Chloride (sold as "Turbo Calcium") you would get leftover Chloride ions in your tank along with your Calcium ions. If you used Calcium Acetate, you would have leftover Acetate ions.
Calcium Hydroxide, or Kalk, is often chosen because the two hydroxide ions (OH-) left over are beneficial to your tank.
When Calcium Hydroxide is slowly dripped into the aquarium, it disolves into Calcium ions and Hydroxide ions. Then it captures Carbon Dioxide (CO2) from the water and combines it with the Hydroxide ions to convert it to Bicarbonate ions. This process can be summed up as chemical equilibrium equations:
Ca(OH)2 <==> Ca++ + 2(OH-)
Ca++ + 2(OH-) + 2(CO2) <==> Ca++ + 2(HCO3-)
The (HCO3-) is what reefers call "Alkalinity," which is important because it protects the tank from pH decreases due to the acids produced by living beings as they breathe and eat.
All the commercial Calcium-raising products like liquid Calcium and two-part Calcium additives are based on variations of these Ca++ bearing chemical compounds and their ionic reactions.
You can buy dry Calcium Hydroxide either as so-called Kalkwasser mix, or you could buy it from a chemical company as lab-grade Ca(OH)2. Getting it from a chemcial company is often actually cheaper.
[ August 10, 2001: Message edited by: BReefCase ]
