This is some rust stains from the pool guy spilling a chemical (hydrochloric or chlorine). Acids can activate the iron in basalt and I am cautious for cleaning with an acid but there is grout stains and minerals. Did some tests with a mild acid to see if any oxidation occurs over the next week. The grout stains (photo 2) probably won't come out anyway because it is so acrylic laced. Did a Klenztone sample and that worked great but hate using that stuff unless I absolutely have to.

Thoughts?

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