Glad to see someone posted an article regarding this. I've always preached "current kills, not voltage". The only thing I'd consider a grounding probe for is to detect whether or not your other devices are putting out stray voltage (potential current) -- so you can replace those devices. There is a ton of electical equipment surrounding your miniature ocean. A seriously dangerous combination.
I liked the note about fish swimming away from, or avoiding current flows (current being electrical, not water motion) -- very interesting thought. I've noticed fish will stay in certain areas due to rock formation, lighting, and water flow -- electrical, hmm. Any daredevils out there feel like experimenting by putting a tiny amount of current through your water to see how your fish react??
Seriously kidding of course.