Oxalic acid mixing ratios for iron stains on concrete

The above pic is before oxalic;

The top of this photo was treated with 1c/gal,
The bottom of this photo was treated with 1/2c/gal.

Reckon I’ll be goin’ with a full cup henceforth!

Question: is oxalic OK on 1)steel lamp posts, 2)vinyl siding, and 3)galvanized steel?

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