Yes, you need a ground probe which is there to save your life. Forget the induced voltage which will always be less than 108 volts. If it is 108 volts or higher, that is a short and if you put your hand in the water it will throw you across the room which has happened to me many times before GFCIs were invented. Put in a ground probe for your own good. I do not like to go on these threads because of all the opinions and arguments from some people who don't understand electricity.
I agree that a ground probe is useful for human health. I have no idea if it helps with fish health with induced voltage, but I'd guess it makes no difference. It won't prevent induced voltages on the other side of the tank.
