Fish Murderer
I worked at a pet store for a long time. We had a Cyanobacteria outbreak and were bleaching individual tanks (once separated from main sump) and then dechlorinating the tanks and testing them before putting them back in with the main sump system.
We had been undergoing the process for about a week at that point, but apparently Ole Red hadn’t been paying attention at all during that time period.
She reattached a tank half-full of bleach to the main tank system. As I walked into the store (it was my day off; I was just there for lizard food), I just see the majority of the fish moving around listlessly. Then they started death-spiralling. I point this out to my coworkers and they start freaking out.
One of them starts dumping bottles of dechlorinator into the system. Meanwhile, Ole Red fishes out her favorite fish, blood parrot cichlids, and starts blowing into their gills, trying to do some weird approximation of CPR. She ends up throwing them into the separate sick tank in hopes of saving them.
Anyway, she killed 99% of the fish and I had to help shovel out their corpses while crying the entire time. She didn’t get fired and never took responsibility for the event. Story credit: Reddit / nerdhappyjq