I've never had better results than when I used kalk. In fact, I've gone back to it recently with this modified reactor:
Pretty simple setup; modified the lid of an old Vertex UF-15 to run 1/4" lines -> built a base with a computer fan -> threw magnets on that -> tossed a magnetic stirring bar into the reactor -> connected to ATO -> BAM!
Edit: Hmm, image doesn't seem to be showing, but if you right click on the icon and "view image", it will take you to it.