[Delphinus]

Sorry if I wasn't clear ... yes I do find kalk to keep levels constant, for the most part (as long as it's being constantly added, instead of a "once per day for a few hours" kind of thing). Just not maintainable at 4.0meq/L alk and 400ppm Ca. More like .. well 2.7meq/L and 330ppm in my "low Ca consumption" tank.

I'm really baffled as to why I had two recent incidents. The first time I did not even clue in to the kalk, I thought it was a light shock issue because I was having problems with my bulbs not firing, and it happened just after I had corrected that. The second time, it wasn't a particularly hot day (maybe slightly warmer than others, but not much), so it wasn't a case of a lot of evaporation causing a whole lot of kalk all at once ... In fact, it was so sudden it shocked me. At 6pm I looked into the tank and all was well. Tank temp was fine. I went to the gym, came back, just after lights-out, and the two purple monti piece were white as snow. Everything else was fine. Other SPS in the tank are some acro frags and some hydnophora in there as well. They were fine. But the monti's looked so bad so as they were completely white. I tested the pH with the monitor and it was 8.6. So I found the cause of the bleaching, I think, but I don't know what the cause of the spike was. I have to assume, though, it was related to the kalk. I've since backed off on how much powder I add to my topup bucket, and am hoping that a repeat incident will not happen. Time will tell.