I have been running a calcium reator (Koralin 1501) on my 200 for the last year, with no other supplements except for trace elements, iodine and strontium. About 3-4 months ago, my calcium and alkalinity started dropping dramatically. It seems that my reactor could no longer keep up with growing sps population.
I then started to drip Kalk for most of my make-up water (2-3 gallons per day). Although alkalinity rose, calcium remained depressed. I finally broke down and used calcium chloride to raise the calcium up to decent levels.
Since then, I have continued to drip Kalk for my make-up water, and things seem to have stabilized. In addition, I have really started to see an increase in the growth rate of my sps.
Nevertheless, I plan to upgrade my reactor (either a new circulation pump, or a whole new set-up) later this year. After that, I will probably eliminate the Kalk.
Mike