No triping breakers ? Are you plugged into a GFCI?
You could look at getting :
http://www.fosterandsmithaquatics.co...m?pcatid=14702
A grounding probe will take out all the stray current, but it would be good to issolate what is causing the problem ... turn everything off and try one device at a time.
However
Do you have cuts /cracks on your skin if so .. its stinging your feeling and not mild shocks.... But a ground probe is not allways going to be a good idea, adding a ground probe, which creates a path to ground actually creates current(flow) within your aquarium. So by adding a ground probe you could be subjecting your fish to electrical current.