Did my first water change today on my 75 gallon tank (about 20 gallons), and went to run some errands. Came back and smelled a smoky smell, like electrical burn smell or the smell when you drill out a screw. I think one of the power heads died, as I received a small shock when I took it out, and when plugged in is not functioning. What concerns should I have for my tank? It is currently cycling, so no live stock. What may have caused this? Anything to do with the water change?