Aluminum Ships, Boats and outboard motors use an "anode". You may like to try that? They are really for salt water which causes electrolysis like other metals can. Electrolysis and galvanic corrosion give me the shivers.
This type of thing. It is cheap to try.
RWB Marine Zinc Rudder Anodes (Pair) (RWB3313 RWB3314 RWB3315) | Boat Warehouse
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