Ragnarok wrote:The oxide coating that forms on aluminium is protective.
Basically the top few molecules oxidise (very fast, given aluminium's reactivity), but then that top layer prevents oxygen getting to the lower layers.
True, however continuous exposure to liquid water, especially an aqueous solution containing small amounts of dissolved NaCl (As would be present here, with Gunfreak living near the ocean), will eventually cause the protective layer to break down and allow corrosion to proceed further into the metal. Aluminum is often anodized to form a thicker oxide coating that will be more resistant to harsh environments.
I wouldn't worry about it though. In this application, the tank should last many years before any significant corrosion occurs.