I use B-Ionic 2 part Ca/Alk. I tried SeaChem for a while but i didnt have great results so i switched to B-Ionic and i've finally been able to get my calcium up to about 400.
Calcium Reactor. But Kalkwasser works well too(or Mrs. wages pickling lime) you just have to monitor it more closely especially your PH. I have the effluent go into the intake of my protein skimmer and that seems to give it some time to settle before reaching my tank.
I've been using Kalk (Mrs Wages) dripped in using a doser replacing my evaporated water. Calc and ALK seem stable, but then again, I don't have much in the way of SPS. I have to start monitoring them closely again since I now have 2 clams.