corrosion and pitting

I have a 100 foot aluminum boat with 4-3412 Cats. It is 25 years old. The bottom plate is 1/2. I have had pitting through the bottom in diferent areas. It seems to be in the bilge area in most of the compartments except the engine room. It has had standing water in it by the looks of the stains. Some of the pits have a jelly like look. Some are just white bubbles. The two inboard engines where not grounded to the hull. Don`t know if that mattered. Also I have a 90 foot steel barge next to me.
What is happening and how can I stop it? Any help would be great!

 

[boo1]

You are starting to develope salt cells, a through cleaning any painting is the best solution. I understand that surrounding boats can introduce stray currents and drive corrosion cells.