A few things first . . . you should get all of your equipment on a GFCI outlet as a safety precaution in case of problems with the water and electricity. You can also get a stray voltage probe to use with the GFCI.
If you do have an electric leak, to find out which peice of equipment is leaking electricity into your tank, unplug all of them, and then plug each piece of equipment back in individually to find the culprit. Then replace it.