Algae with some other stuff (little growth in plaster)

[john.contreras]

Hello,
I am in the process of doing a SLAM on my pool (CYA 60, FC 30), because my pool had a green tint. A day after the SLAM, the pool passed the overnight test, but I had these little black web like patterns in the plaster.
Is this black algae?
Please see attached picture. The growth is the size of a nickel. We only have ~40 of these little webs in the shallow and deep end.
The pool is now crystal clear, but the little webs still remain.
Also, we had the pool re-plasted last year. Any recommendations?
Thanks,
John

 

[Richard320]

More than likely, those are hairline cracks in the plaster and you're seeing efflorescence or metal discoloration from behind.

 

[john.contreras]

Thank you for your input.
Because the pool was re-plastered a year ago, I asked the pool company to take a look. They checked all my chemicals and everything was great. They are bringing in their plaster guy to look at it. They also are thinking the dots/webs may be black algae. The spots have not grown at all.