Electrolysis / Keel stepped mast
Sounds like you''ve got a corrosion/oxidation problem caused by salty bilge water in contact with aluminum. Careful sanding & surface preparation, followed by a coat or two of paint should fix it. Electrolysis is a little different, caused by electrical currents. If you do have electric currents running through your bilge water, wiring everything together will make the problem worse, not better.