Before my reactor I used a Warner two part supplement. Once you get the proper dosage you just add it daily.
You can also use kalk for your top off if you have enough evaporation.
Aragamilk should not work in theory because calcium carbonate should not dissolve in normal aquarium water. Otherwise the skeletons of corals that they have deposited would dissolve. It might have other benefits in the photosynthetic efficiency of corals. (see article below)
CA reactors use CO2 to lower the PH to dissolve the CAO3.
Check out these articles by Randy Holmes-Farley.
http://www.reefcentral.com/forums/sh...hreadid=481425