That's what's frustrating. I don't have anything that really uses CA. I have 2 frags of Zoa's, and no other corals. For over a year, the tank was nice and stable. Haven't changed salt, using Oceanic. It mixes up at 1.023 with 420Ca, 1250-1300Mg and 8.5-9 dKH.
I need to get my own better...