"I have to ask this, assuming the cord to the lamps are two wire how would a GFCI help?"
Perhaps a ground path is provided by the pump and filter, or the air bubbler? Perhaps if the wall and floor got splashed, there was enough leakage current thru the metal studs, or damp plaster, damp wood, or something else.
How long must the current flow before the trip threshold is reached? Would capacitance charging of the floor, wall and cat, be enough to trip the GFI?
