The GFCI does not need or utilize a ground probe to trip so its presence is not necessary. Use a GFCI and forget about the ground probe. There is no data suggesting it will help the health of your fish, and a good possibility it will be a hazzard to your safety.
I strongly disagree.
With a ground probe and a GFCI, there is a path to ground, so any exposed electrical wires will leak some current into the water and out the ground probe, triggering the GFCI.
Without a ground probe and with a GFCI, there is often no path to ground, so the GFCI will not trip until there is a path to ground.
The first thing to provide that path may be your body. I do not want to test the expectation that the GFCI will trip in time to protect me. I'd rather it trip as soon as there is the potential for a problem of that sort, and a ground probe allows that.
Further, if there are exposed wires in the water (like a broken heater or powerhead), they may release copper or heavy metals and not actually trip a GFCI since there is no path to ground. With a ground probe, such an event trips a GFCI immediately, alerting you to the problem earlier than if you had no such probe.
and a good possibility it will be a hazzard to your safety.[?B]
What scenario involving both a ground probe and a GFCI endangers your safety relative to a GFCI alone?