Black stain in metal Won’t come off

Hit this metal siding with house wash mix, then upped it to 3.5+ %. Stain didn’t budge, my buddy thinks it’s simply where it isn’t painted but it looks like a stain to me. How can I get rid of it?

Did you try a soft brush or a rag? On metal, certain stains take some agitation.

Try diluted muratic acid and a brush to it.

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About to try La awesome with a brush then rinsing.

Looks like ‘reverse’ tiger striping, rainwater deposits impurities on the metal.

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