I suspect the two solutions would precipitate together forming a crust of calcium carbonate at the bottom of the ATO reservoir. If you'd like to understand reef aquarium chemistry there are many well researched/written articles available for free online.
http://reefkeeping.com/issues/subject/chemistry.php While the conventional 2-part system cannot be applied directly to the ATO system, Kalkwasser can be in many instances with only a few downsides.