You have to be careful when you use a grounding probe. Yes, they offer safety for the reefkeeper and the livestock. But they can also be deadly to the livestock. An example: You have a small reef tank with a sump, run off a powerstrip that is plugged into a GFI and a grounding probe is used, connected to the same ground the GFI uses. Lets say you have a submersible powerhead. It's a little old and the seal around the case starts leaking just the tiniest little bit. Not enough to hurt either the reefkeeper or the fish, but enough to trip the GFI right after you leave for work... Now the tank sits still, no heat, no light, no water flow all day long. By the time you get back, all your fish are gasping for air, corals are melting and the tank is either crashed or on the verge.
Long story short, be careful what devices you put on the GFI. If you take your whole tank down, it won't work out well for you...