Mr. Jankowski, how about measuring the CURRENT instead of the VOLTAGE?

If you do not have connection to ground you WILL NOT FEEL the voltage.

Have you ever observed birds sitting on a high voltage power lines?
They do not care about the voltage to ground when they do not touch
the ground. The same is with your fish: they do not care about the
voltage between the water and your copper pipes BECAUSE THEY DO NOT
TOUCH THE COPPER PIPES.

If you were able to attach your voltmeter between the bird's wing
and the ground you would measure thousands of volts. Would you consider
a good idea to connect the wire between its wing and ground to "neutralize"
the voltage? Think about it... what current would flow from bird's legs
to its wings after you connect your "birds grounding probe"? :-))