It's not even the death of a fish.
It's that I just broke a piece of my thermometer while using it to help clean the filter, as I always do, and the red liquid went everywhere. including the filter pieces.
Meaning, my filter is in the garbage now because I can't imagine it being remotely close to usable again.
It was one of the best filters I've ever had/used, and I've recommended it to everyone. My fish were great with it, and it was perfect enough it didn't need to be baffled. And now, I need to do a re-cycle
So thank you filter, for helping for so long :<