Stray voltage causing HLLE, (Head and Lateral Line Disease, which I believe is what you mean by LLD), is one of the presumed _possible_ causes of the disease.... It is _far_ from being proved to be the cause. Inadequate diet, odd water conditions, stray voltage and several other causes are all potential causes but anecdotal evidence to date both proves and disproves each and every one.
If you have implemented measures to eliminate the stray voltage then it is probably not the cause... It's something else.... Unfortunately I am no brighter than everyone else so I can't help you much further than that. Vary the diet, (heavy on the veggies some people claim to be useful), you have the strayy voltage taken care of, keep up the water quality and then it's up to you....
Final Disclaimer:-
Even with the worst cases of HLLE, of which I have seen some pretty horrific cases, the fish often live for years. It is generally accepted that HLLE is not a killer of fish though if other things are wrong it may be contributory.... You might want to proceed from that point of view.