Its used to bump up calcium levels where as Kalkwasser helps maintain Calcium and Alk. You also can dissolve it in RO water and add directly to the tank unlike Kalk which should be dripped or added to ATO.
It's calcium chloride. Go to www.bulkreefsupply.com, and you can buy buckets for the price you paid for a cup.
The stuff works great if mixed and dosed properly.
Calcium chloride (aka 'turbo calcium') is much different than calcium hydroxide ('lime' or 'kalkwasser'). The former is soley a calcium source. The latter is a balanced additive that raises both calcium and alkalinity. If you're trying to tweak your calcium up or just focus on the calcium side of the equation, use the former. If you're trying to maintain an already balanced cal/alk you could use the latter.
BTW....9lbs of calcium chloride sells for about $7 at my local Home Depot....Prestone Driveway Heat.