Due to my old friend, Mr. Kalkwasser!! I began adding kalk to my water top off reservoir and it has kept my alk and calcium steady over the past few weeks. I turned off the reactor a couple weeks ago and wondered if the kalk would be enough for my corals. Sure enough, the levels have remained rock steady! My alk sits at 10 dkh and calcium at 400+. Hopefully, the kalk will be sufficient enough for the corals over the long haul.