Electrical Leakage in Saltwater Aquarium

I felt pin poking into my fingers when I touch the seawater in my aquarium.  Immediately, I know my pump is leaking out electricity.  I have two pumps.  The big pump is inside the aquarium and the small one is outside.  So I assume it is likely to be the big pump.  I used my multimeter to measure and indeed the voltage is there when I used my body as ground.  So I took out the big pump from the tank expecting the voltage to drop but it didn't.  What a surprise!  The small pump is like waterfall and is not in the water at all.  So I assume even if it is fault, the electricity will not travel out.  I was so wrong!  When I took out the waterfall pump, the voltage drops.  So I know it is the waterfall pump that is faulty.  It is quite interesting as the electricity has to travel out of the pump through the water falling into the aquarium.  It is still possible as saltwater is a good conductor of electricity.