My uncle is an electrician for about 25 years now and i asked him about a GFI outlet for my tank and he told me that it probably wasnt a good idea because they tend to trip too easily and if this happened when you arent around for a period of time it could be the end of all ur fish.
I think having a ground probe is enough for stray voltage.
That is not good advice. The little grounding probe is NOT enough to save your life!! It's job is to remove stray voltage from heaters, pumps etc... to protect your fish from electrical related injuries. It may be enough to protect you from small leaks, but the GFCI is a MUST-HAVE.
For those thinking that they trip too easy, causing a possible loss of life to your fish...Think about your own life too. Is it worth the trade off?
As far as them tripping easy, I have never had mine trip yet accidentally, but I do have my inline (unsubmerged) return pump connected to a standard outlet and everything else to the GFCI.
If it does trip, then the pump will continue circulation and still produce enough heat to maintain my tank.
Not using a GFCI, is just plain silly!!