"david" wrote in message ...
As an electronic engineer do you agree that the probe will not
drain to ground minute voltages (or rather currents)? Strange...

In my opinion it will drain those currents and this is not good.
Yes, it is good in the meaning the probe will trip the breaker...
But currents will create unhealthy environment for tank inhabitants.
Without the probe there would be no stray currents in the tank
since relatively to ground it would be insulated by glass&wood.

but then in the sea it would be connected to ground.

Where have you seen sea waves made with an electric powerheads?
Do you understand, that there is a huge difference in terms of
electric environment when you compare fish tank and any ocean?
Water movement are powered with gravitation, termal events, but
not electric powerheads which could leak electricity to water.
The same situation is with lights. Fluorescent tubes leak a lot
of electricity to the souroundings, including tank water...
Especially, when they do not operate near grounded metal reflector.
Have you seen parts of the ocean lighted with fluoro fixtures? ;-)

My opinion is that we cannot blindly copy one feature of the ocean
(water is grounded there) without contemplating the consequences
of this kind of decision in our artificial fish tank environment,
normally FULL OF INDUCTED or LEAKING ELECTRICITY from many electric
devices making it posible for the fish tank to work.

how do fish senses like sharks work ? :-) ?

Sharks/Rays are very different from an ordinary bony fish like tang or clown.
I would not torture any shark in a home aquarium... I have read stories about
fast growing 60cm sharks in people basements swimming in a 4 metter tanks
and I got strong recollections about a goldfish in a 1-litter fishbowl :-((
With a big difference that shark psyche is much more developed making the
comparison even worse for a very complicated fish like shark.