Grey stain on bricks

[Spencer]

Anyone have any idea why the red bricks on this fountain would have a grey stain? Is it from the fountain water? What do you think would take it off? Safe Restore? Should I use regular house wash on the rest of the building? It is a very large complex and I want to price it accordingly. I have never cleaned this much brick. Thanks for any help.

 

[PowerWash Pros]

Limescale and Efflorescence, these are my guesses.
Some sort of algea on the bldg part...

Celeste is a good person to ask about brick!