electrically inept
 

Is a grounding probe in the sump sufficient for the whole system?

why are you using a grounding probe? what does it achieve?

A grounding probe is supposed to get rid of any stray voltage from heaters, pumps, etc. which can cause stress to livestock

it depends on what equipment is leaking. If the powerheads are leaking voltage, then in tank will be better, but in most cases, in the sump will work fine.

and trip off your GFI.

Would think with the conductivity of SW, one would be enough.

Yes, all the water in the system would be electrically connected. So it doesn't matter where you put the grounding probe.

You still need GFI, though. In fact, I've heard that having the GFI might be more important if you have a grounding probe.

gfi should be sufficient to detect any stray current through the water, if i had current leaking from a device in my tank it would be time to replace that device, leaking current can be dangerous and usually means the devices integrity has been comprimised.
GFI are set to trip at a deficit of 4mA so if any current is leaking even not on your ground rod then it will trip, GFI does not need the current to go through a ground wire to trip the device.
GFI looks at hot and neutral and compares them, if they are not equal the device trips, they acutally have nothing to do with the ground connection, other than that is the usual path to ground in a fault, but in a tank it could be other paths to ground, including your arm.

Thanks people. I have GFI as well, so I'm really covered.

Lance