In one week adding a reactor that is increasing calcium = stability? That is the definition of "lack there of" over that short of a period of time IMHO, but not a bad thing. I think it a matter of giving your corals more calcium that they were not getting before, although they found a way to balance. It seems your corals are consuming it as fast as you are putting it in if you didn't see much of a change testing, but are seeing more growth. My tank does the same when I change media in the reactor, or up the flow rate. I'd let it go for another week or two, then up the flow rate (which ups the CO2 used etc) slowly to keep the balance but introduce more calcium. When your tanks are maxed out testing will show it rising. Then let it stabilize. Your growth rates will go up. This is what mine seems to do.