Removing Mineral Stains From Soft Maple

If not oxalic acid, I have had good luck removing water stains from cherry with Dawn w water and a stiff plastic bristle brush. To make sure I didn’t just get a new line, I lightly wetted the entire piece after scrubbing.

-- Mike (near Boston) ... Laziness is the mother of invention, necessity is the mother of exhaustion - me

You don’t have to douse the entire piece of wood in oxalic acid. You can just apply the solution to an area you want to treat, though any method you do a spot treatment with could cause a lighter splotch that could be visible later so you might want to try the spot treatment on a scrap just to see what affect it has on the appearance.

I assume you have tried just sanding it to make sure that it is not just on the surface.

-- Nathan, TX -- Hire the lazy man. He may not do as much work but that's because he will find a better way.

Oxalic acid will remove the stain but, as Nathan counsels, try it on some scrap, first.
You might try plain old bleach first, though.

-- Gene 'The true soldier fights not because he hates what is in front of him, but because he loves what is behind him.' G. K. Chesterton