Hi,
When you were messing with your tank, did you wash your hands all the way up to your elbows?
If it wasn't the rock causing an ammonia spike, then you may have had soap or something on your hands. Total die off is caused by something.
What were you eating, what were you handling, could anything have fallen into the tank? Did you use a rag or sponge that may of had something on it?
Ask these questions of yourself and try and figure out the mystery, because you don't want this to happen again.
I poisoned my tank once because I was using Puff Plus with lotion to wipe my nose.