If you have any device leaking elektricity to the water, and you are
affraid of negative effects on your tank inhabitants, the grounding
probe will make things even worse. It will INCREASE the current
flowing from the failed device to the ground through the water column.
Without the probe, the resistance of glass, wood is high enought
to make the current flow almost zero. The probe will lower this
resistance to zero and current will be limited only with the weak
resistance of broken insulation of the device.

If you narrowed the problem to the light fixture I would look to this
really closer. Does it have metal reflector? Is it correctly grounded?
Lights usualy radiate some electricity to water, but if the fixture
is designed correctly it is negligible.

Do one test: disconnect the probe from ground and put a multimeter
in series with it on a AC current settings. If you measure less then 1mA
I would not worry about. If it is more than that I would fix your lights.
Let me give you an example - the original fluorescent fixture from
CustomSeaLights causes readings on a level about 0.2mA. DIY
fixture I made with my friend gives reading 0.8mA when one lamp is
on and 1.6mA when both lamps are on. This is a reason for us to
redesign reflector and replace glass mirror with grounded polished
aluminium.

In your case I would fix the light fixture and I would get rid of the probe
for sure.

In a matter of your GFCI plug - what is it rated for? 5-6mA?
Or maybe bigger? 1mA current is detectable by human skin. 5mA is
already very painful. GFCI plug will not react to very small currents.

wrote in message ...
Just wondering here...I put a ground probe in one of my tanks and
hooked it up to a GFCI outlet. I was feeling some shocks when I
touched the water. I narrowed the problem down to the lighting.
Anyway, the GFCI never tripped. I thought aside from supposedly
ridding the tank of stray voltage, that it would also trip the GFCI
when the water is touched. I guess not? What's the deal?