I wondered the exact same thing a few months ago when I started dosing kalk. I add it to my top-off, which drips from a 5gal bucket through an I.V. dripper. I started with a bucket of 1tsp/gal, then tested my alk/ca every day and added 2-part solution to keep the levels up. Each time I topped off the 5gal bucket, I added a little more kalk until the levels stabilized and I no longer needed to add 2-part. After a few weeks I found that ~2tsp/gal works for me and keeps my levels stable. Every once in a while I'll add some 2-part for the trace elements, but the alk/ca stay stable with just the kalk now.
Hope this helps!