The best way(other than a calcium reactor) I've found is to approach it from 3 seperate points....
I use seachem products to build levels of calcium/alkalinity/ph...
reef advantage to build calcium levels(400-450 ppm)
reef builder to build alkalinity levels(2.8-3.5 meg/l)
reef buffer to maintain a ph of 8.3
it has been my experience that all these levels should be stable or they can have adverse effects on each other.