I understand a full-blown zap in the water...but I am wondering about small amounts of current which could harm corals and fish over long periods of time.
I've heard that stray voltage can cause HLLE. I have probes in the sumps of my two big tanks and still get shocked from time to time. It doesn't seem too logical, but my lights seem to add alot of stray voltage... All I can think of is there is a line of salt creep somewhere that is giving a pathway. I measured with a voltmeter/ammeter and with everythign else in the tank off but the VHO's, I was still getting measureable levels of voltage. I think I should investigate further...
On another note, I had seen an artcile where somewhere Indo Pacific, they were introducing small amounts of voltage to reef areas where they placed frags and saw better growth than the frags that were not near the source of voltage. Seems dangerous to me. Seems like electricity and electric conductors shouldn't mix, though...