cil weed and feed and stain

Specifically, what product did you pour?

Try a metal polish, automotive rubbing compound, toothpaste, baking soda, or other mild abrasive to remove the stain but only if you trust that doing so will no worsen the appearance. A very fine steel wool, not a scouring pad, may also help.

Try in an inconspicuous area of the metal sink first.

-- Tom

I just checked the label and it has a small amount of phosphoric acid in it. So I suppose it's permanent?

Not necessarily. It's probably only on the surface of the metal sink. Getting the polished area to blend in to the remaining sink metal is likely to be more difficult to achieve than removing the chemical discoloration.

-- Tom