Try an acid and a scotchbrite.
DO A Test to confirm the results and procedure.
Polishing would be a big step for that project, and it would eventually come back, even if they filtered the water. I would imagine having to start at as low as 400g and take it back to 3000g+ before polishing with Granite Polishing Powders or Compounds.
Once again, do a test to confirm results and procedure.
Good luck

Sent from Bob Murrell's iPhone
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> On Mar 11, 2025, at 7:58 PM, Christian Maniscalco - christian at southernsurfacecare.com (via sccpartners list) <sccpartners@stoneandtilepros.simplelists.com> wrote:
>
> Monday.