Also what kind of coral are you keeping and you plan on keeping in the future? I heard it's easier to keep up with the calcium demands of a heavily stocked SPS tank with a calcium reactor.
what size is the tank?
I have a JBJ top off that is only used for top off. I maintain my calc/alk through DIY two part. Very cheap and more reliable and controllable than kalk if you get your calcium from littlesilvermax (on the forums here)
here's a good recipe:
http://reefkeeping.com/issues/2006-02/rhf/index.php#5
and a good calculator:
http://reef.diesyst.com/flashcalc/flashcalc.html