Many of my brown trout fishing buddies now run the Scotty downriggers with the Black Box hooked up, I printed out the article they had about the Black Box which was 26 pages. Here is the best analogy I have heard, the fishes head is the negative magnet and the cable is the positive. When the cable passes the fish the head is pulled toward the cable and the fish follows, too low and you cannot draw the fishes attention and too hot and the fish are spooked. Some fish like kokanee are real easy to catch with a Black Box. The hope of the box is that you will not have to run your lines as far back, but let me tell you just because you have positive ions in the water does not mean any big old brown is going to throw caution into the wind and follow the ions. Talking with a guide in central Oregon he mentioned the dramatic improvement in laker fishing he has had with the Black Box. Most guys are now running Scotty for this reason, Cannons have a Black Box built in but you need a volt meter too.
As to the other part I was chatting with a well known guide from New Melones, on the prefish days for the big kokanee derbies he runs an Aqua View off of the downrigger to get an exact understanding of what size kokes are being marked. When asked about trying to controll the amount of ions the Aqua View produces there was no way to do it at the time.