Are you sure you need to do either? Dosing with a regular liquid calcium supplement works fine for most people. Usually you will only need a calcium reactor if you have a tank full of SPS corals. Dosing with kalk can be tricky, and disastrous if you screw up (I recently had two tanks crash due to an accidental kalk overdose).
I use Kent Turbo Calcium, just a liquid additive. It works just fine. And for a lot of tanks, regular weekly water changes is enough to keep the calcium up.