HEAD & LATERAL LINE DISEASE

Head and Lateral Line Disease
A disease brought on by poor water quality, nutrient deficiency, or possibly parasites. Some aquarists argue that stray electrical currents in the aquarium water from electrical devices can also bring this on. The symptoms include ulcers/holes in the head area, and/or erosion of the lateral line along the dorsal side of the fish. It's best to make an attempt to improve aquarium water conditions, dose food with vitamins, ground electrical currents, or medicate with Flagyl (a freshwater remedy for hole in the head).

Interesting link that partially addresses HLLE and stray voltage.

http://article.discusnews.com/cat-02/strayvoltages.shtml