pickling lime or kalkwasser is calcium hydroxide do a search on here there was a big thread on it not to long ago in fact here it is
pickling lime instead of kalkwasser
here is a good place to buy in bulk
Two Part Solution, Discount Calcium and Alkalinity Supplies
Limewater also contains particulates that are critical for understanding how metals are removed from solution. In addition to undissolved calcium hydroxide, limewater often contains calcium carbonate particulates that arise from the reaction between atmospheric carbon dioxide and the limewater.
When carbon dioxide is dissolved in water, it hydrates to form carbonic acid:
(4) CO2 + H2O à H2CO3
In limewater, where the pH is above 11, the carbonic acid dissociates to form carbonate:
(5) H2CO3 + 2OH- à 2H2O + CO3--
The carbonate can then combine with the calcium in solution to form insoluble calcium carbonate:
(6) Ca++ + CO3-- à CaCO3 (solid)
This calcium carbonate can be seen as a solid crust on the surface of limewater that has been exposed to the air for a day or two. It also collects on the bottom of the container.
Chemistry and the Aquarium