as an electrician i would highly advise against on, gettign a probe you're more then likely going to kill y our system with electricution.
stray voltage sitting in the water is making the fish the same potenctal when you add the probe you are finishing a circuit which will pull amperage through. the amperage going through the system is watch will do all the damage so frankly as far as i'm concerned a grounding probe is only good for the manufacture who is trying to make money off you.
if you're worried about shocks and voltage leaks then invest in a GFI outlet to plug you electrical into, what will sense a difference in current which will trip the GFI and let you know there is a problem somewhere.
