That doesn’t look like it’s biological to me. Try dropping some acid on the white spots and see if it fixes it looks like it might be some kind of salt deposit

Sent from my iPhone

On Sep 27, 2018, at 8:40 AM, Great American Stone Care <info@greatamericanstonecare.com> wrote:

Good morning everyone! :) 

I have a customer that has what looks like a microbial growth on her Flagstone counter tops. It was installed 4 weeks ago and the black spots began to appear about a week ago. 

This counter top is located on the customers back porch. 

What product and process would be best to remove this and keep it from returning? 

Thanks in advance. 

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