What is the best way to treat corrosion.
That's not corrosion, it's patina!
Buddy : What is it??
It's the filter for the A/C unit
Buddy
It looks like a non issue to me.
If you'd feel better you could clean it up by power wire brushing or maybe C-L-R would work? and spray it with a clear coat. I believe that CRC has a suitable industrial type anti corrosion clear coat.
Buddy : You also might try Lime-a-Way (more friendly to copper/bronze) to clean it up and then spray with T-9 Boeshield.
A thought