The links I posted in Post #5 contain valuable info regarding grounding probes and more importantly GFCI devices for your safety. Definitely worth a read, they're a little technical but fairly understandable. I'm reasonably confident that it's a reliable source of info, the guy is/was a Research Engineer with Georgia Tech Research Institute & Associate Professor at Georgia Institute of Technology. He's got a little bit on the ball, I'd say. The page on his aquarium build is also a very good read with some innovative ideas. A bit dated perhaps, but great info nonetheless.
http://angel-strike.com/aquarium/MICHELSONAquarium.html
Sticking your hand in the water while getting a buzz to isolate faulty components in your system is not the way I would go about problem solving. There's a rather important distinction to be made between a circuit breaker & a GFCI. A circuit breaker is designed to protect your wiring from catching fire & burning your house down. A GFCI device is designed to protect you from shock, principally when dealing with electrical components in and around water. If you're not using GFCIs for your tank, you'd be well advised to invest in one or more depending on the number of items running your system.