Lime is what is generally labeled as kalkwasser at the LFS. The clear liquid that is used is called limewater( kalkwasser in German) for obvious reasons. This is a very old technique for reef keeping that I really believe in. It isn't good for initially raising cal and alk, but it's excellent at maintaining them. It also produces a form of calcium that my corals seem to thrive on. It must be added very, very slowly, usually when the tank ph is lowest. Some add it to their top off water. I use a doser with it.