Here are two articles in plain English which helped me:
http://www.melevsreef.com/calcium_reactor.html
http://reefkeeping.com/issues/2007-12/pr/index.php
At the end of the day, a calcium reactor is pretty simple: it's merely a container where coral skeletons are dissolved using CO2. There are basically two points of adjustment you have to worry about
: bubble rate and effluent drip rate. Different brands of reactors have different levels of complexity of set up and adjustment. European ones like Koralin and Schuran have a reputation of being tricky and more complicated to set up and adjust. I have a GEO 612 and it was a snap - I had it running in about half an hour and dialed-in within a few days.