Tonight when I was at lowes browsing the isles for anything related to aquariums I strolled over to the gravel/sand section to see what they had. I found a 50 lb bag of "High Calcium Hydrated Lime". I'm not a chemist but isn't this kalkwasser, a bag was torn in a corner and it looked exactly the same. It was around 7 bucks for a 50 lb bag and something like that would last forever. Here is a link from a search I did with the above title. Hope this is it.
;)
Ben

http://www.chemicalland21.com/arokor...0HYDROXIDE.htm