This question has probably been asked before, but is it true or a myth that one can get possibly electrocuted by having your heater or other electric device plugged in while working on your tank?
I had one with a minor short that gave me a bit of a zap before I replaced it and have seen scorcthed drapes from a shattered one, a quick arc occured as the breaker tripped, it was a steel framed tank.
Faulty equipment can leak current.. and the current can kill. I thin its a good habit to install grounding probes into your tanks so that stray current does not flow to you. However checking all equipment regularly and buying reliable ones like eheim is still the safest method.