Tank nuked...

I don't think it was the Pump myself.. If that pump had put that much amperage into the water to kill all fish that fast then you would have been knocked across the same room when you touched it or the water while it was plugged in . Not to say you already do not have stray voltage .. But Not that fast.. Voltage stings and annoys and pull the animals down over time Amperage kills Now.. I thik that added flow disturbed somthing in the system.. Opened a pocket of somthing bad.. Maybe

 

That's right.

Birds sit on high voltage wires all the time. The fish would just be in it. They do not have their feet on the ground.

Electric motors have magnetic fields created with the alternating current in field windings. This 60 cycle harmonic can be felt by the fish and some fish are sensitive. Putting all your electronic gear into a sump is a good thing.

Flourecent lights give off 60 cycle wavelenghts. Go into a brightly lit (with flourecent) and you can feel the difference.

 

Did you rinse the powerhead before you stuck it in your tank?