Hello Partners, have a Shell Marbella limestone type stone paver tile that's sand set on south exposed patio. The install is 2 years old and a year into it the customer noticed a black stain that seemed to be coming from underneath the surface. It's know very pronounced in some areas (see attached photos). It's more obvious around the pool, especially the portion behind the pool which is always in the shade.
I have sampled it with cleaners such as high ph cleaners, a degreaser, diluted bleach, algae cleaner and also agitated with brushes and a 240grit brush on a makita. It looks better only after scrubbing. This is problematic due to how soft the stone is.
Wanting to find a chemical that reacts or breaks down the black stains.
