I'd probally stay away from it, cause generally if it says it "contains" something, that means that it also contains other things... You might be able to call Aquachem and ask them about the ingredient list though
Seachem makes a variety of products for raising calcium
kalkwasser, reef complete, reef calcium ect.
Is this for a marine aquarium? I'm not very familiar with dosing for calcium in the freshwater aquarium