I use GFCI -- 2 of them on my tank. One for the lights, and one for the rest of the stuff. Electronic ballasts can be tricky with GCFI and if I turn on too many lights at the same time, it will trip. If I stagger them the GCFI is alright. This is because of the RF filtering that bleeds some current and when too many turn on at once, it bleeds enough to trip things. I use it for safety. Basically, if I stick my hand in the tank and there is current flowing through me, the GFI should trip. I use two of them to keep the pumps going if the lights should ever trip things.
I don't have a ground probe, mainly because I'm not so sure they do anything that I _really_ need (there is a big debate), and also because I never got the gumption to go out and get one and hook it up.