Ground Probe ?

It is a heated subject. With the little E & M I've had, the only thing I can recommend is to stay away from them. Reason being is that by placing a grounding probe in, you are providing a means for that stray voltage to flow, therefore providing a current. The current that is flowing through it, combined with the voltage, is the issue. Voltage by itself isn't as much of an issue and seawater actually has a natural electrical potential due to the movement of ions in solution (which creates a very small magnetic field, too). Also, even the lights, ballasts, etc. will emit an electric field, inducing voltage in the water due to the presence of all those ions. So basically, any tank will always have some static voltage. It just seems like a bad idea to provide a means for it to move, though. Again, though, that's just the theoretical side from what I can gather.

Here is my point of view on the subject.. as long as you have nothing in your tank that has power, then it is a good idea to have a grounding probe in the sump, but if you have power cords in your tank for power heads and heaters, then it is not a good idea. I do think grounding probes help a ton with things like HLLE. Seen it solve HLLE issues on tangs in under a week on many occasions when nothing else was done.. and almost immediately Tangs seems to act a little calmer when a grounding probe is added. Don't ask me the scientific reasons for that because I really don't know.. I just know I have seen it done dozens of times (my LFS always recommends grounding probes) and every time the customer would come back stating it solved the problem. After enough of those success stories you have to start to believe the grounding probe is helping.

On my setup, I purposely made it where the all my electrical equipment that is in water is in my sump, no cords in the tank. The hopes is, any stray voltage caused by pumps and heaters will go to ground within the sump before it gets back to the tank. I tested this by stopping my return pump and testing stray voltage in the sump with a multimeter, about 10v, then tested in the tank with the lights on, 0v.. put in grounding probe in sump, no more stray voltage. So I know the pumps and heaters in my sump are causing the majority of the stray voltage and I am grounding those hopefully before it gets into the display tank... not knowing 100% how the current will flow I can't guarantee it is doing exactly what I want, I just know I don't get shocked at all with a grounding probe in the tank, but will get shocked if I kneel on a wet towel and stick my hand in the sump without a probe.

Nope, only powerhead I have is the Vortech MP40w and the power is on the outside of the tank on those.