I use a calcium reactor and Littlesilvermax's magnesium. I used to use a kalk reactor but with the zeovit system it is not recommended. I test the alk once every few days (because it's really easy to test) to make sure my calcium reactor is maintaining my levels. Magnesium I test once a week during water changes to see if it needs "topping up".

I use both a Calcium reactor and Kalk. reactor. My yearly costs are considerably cheaper then what I budgeted out for a dosing system. I also run magnesium in my Calcium reactor, which generally gives me a 'set-it & forget it' option.