How did your reef tank crash?

[Lampshade]

Voted for multiple, because it was multiple.

Power outage for 12 hours in January, caused die off. Excess nutrients cause macro algae to grow like crazy, fill refugium andcaulerpa to go sexual. This caused another cycle, too long for SPS, so there was SPS die off. Calcium reactor was still outputting the same (I did sometihng stupid), and my levels went nuts. API Test kit still showed 7KH, i thought i was good. Got water tested at LFS, 14DKH, bought another test kit(salifert), and showed 14 as well. (Other) Ouch, lots of water changes, small issues with salt being high KH (12KH in new water), but didn't cause too much issue, got more salt and rolled the bucket better this time :P. So things are finally looking up and i wake up to find thatmy kids put a graphing calculator in the sump, complete with batteries the day before. (my fault too, i left the fish room door unlocked with a 3 year old and a 2 year old) Big reset button again for the tank. Overall, lots lots, learned lots, and now things are going GREAT. My tanks still got some aiptasia issues, but coral that had completely browned out(bleached then brown, totally dead) is coming back. I went through and purged the dead-dead stuff, the recovering stuff is looking good.