[Magma]

few things that worry me so lets start at the top and work down

Stray current refers to flowing electricity. It is typically harmful to humans at and above 6mA [1]. A properly functioning tank should not exhibit any measurable stray current (< 1mA). Stray current may or may not trip a GFCI receptacle depending on the path it takes.

This isn't right at all, current kills, end of story even in the mA range you can get a poke which will set your heart off rhythm and die later. I pulled this from a few of the electrical modules I still have:

Currents of less than 0.02 amp may produce sensations ranging from tingling to sharp pain. A more serious effect occurs if the current causes muscles to contract. A person touching a live wire with their outstretched hand may literally not be able to let go of the wire due to the current's effect on the muscles. Experienced electricians who must sometimes deal with wires which may be live always use the backs of their hands to move the wires; if a current were present, the contacting muscles would cause the hand to pull away from the wire. Currents from 0.03 to 0.07 amp will begin to impair the ability of the person to breathe.

The most dangerous range of currents is from 0.1 to about 0.2 amp. Currents in this range can cause death by initiating fibrillation (uncontrollable twitching) of the heart, which stops the regular flow of blood to the rest of the body. Currents much larger than 0.1 amp do NOT result in fibrillation and instead stop the heart completely. If the duration of the current is short, the heart will usually start to beat by itself after the current is removed.

So in other words if your not sure don't touch, it doesn't take much to end up in a serious situation which could lead to more problems or death.

So next up....another problem

Ensure all equipment is connected to a GFCI outlet. While this is not required for to measure current it will significantly reduce the risk of harm and/or death if a mistake is made.

If your not an Electrician this is a problem because as every sparkie knows you need to use a clamp on amp meter to measure the current this involves taking the plug out of the box and clamping onto the hot conductor then turing everything back on to measure the current, or a really expensive meter which you can hook up in series with your setup. Just dont do it because unless you know what your doing you will get hurt.

Finally

== Recommendations ==
An aquarium should have no detectable stray current. Eliminate all sources of stray current. Consider installing a ground probe (in conjunction with a GFCI outlet) to identify stray current sooner. Stray voltage can be safely ignored provided there is no stray current.

Stray voltage can be just as bad. As a human your body as a ridiculous high ohmic value which allows us to touch wire which has potential voltage on it but again unless you understand how you are able to touch the wire don't do it. Also have to be aware that if you skin is wet your resistance drops significantly and if you have a cut your ohmic value is now no more than a light bulb.

Dont get me wrong I have been poke a few times from different things anything from 120v up to 347v its not fun. But you have to be able to say I know what im doing and I bet my life on it. Also really shouldn't be using a ground probe to solve the problem IMO, if you know you have a voltage leak then get on it and find it and fix it because if you have a leak how do you know in a day, week or month that something isn't going to go wrong and you end up with a blown pump or busted heater? Find the problem by turning on things one at a time once that's done remove the faulty equipment and go from there.

Edit: forgot to mention you should add in there "What ever the guy at home depot tells you, dont listen to him hes not an electrician, hes customer service."