I finally figured out the whole mystery of stray voltages in a tank. Don't risk death. Use a ground probe and GFI socket. Your tank is not worth your life. It happens all the time.
Someone takes a multimeter and measures the voltage between their water and earth ground.
They get 30 to 60 volts and then panic, thinking that this is somehow bad and that they should do something to get rid of it. I'll cut to the chase here and say that both of these are incorrect. Induction is not the cause of stray voltages. Ground probes are not going to remove it. And it cannot possibly be the cause of fish deaths.