surface damage

Hi everyone, I’m new posting here but read others post often. We just had our pool area and pool itself remodeled. We had chosen Stonescapes mini pebble aqua cool however the company ended up installing Marquis Bluestone (we had gone back and forth between the two and the company got...

I seem to have black/brown patches on the side walls. The water itself is crystal clear. I see these patches for some time now and slamming doesn't seem to help. I'm not sure if its black algae or the surface itself is damaged. Attached some pics here of the walls. Any thoughts on how...