Black spots

[Yelimex]

A few days ago I started spotting a few of these black dots, mostly on the steps. I was able to scrape one with my finger but when I tried to use the brush, it did not remove them. Any advice?

 

[mknauss]

Scrape one off and smear on a piece of white paper. If it smears green, it is black algae.

 

[Yelimex]

Yes, it smeared green. Do I need to SLAM?
How and when should I try to scrape/remove the black dots?

FC 5.5
TA 100
pH 8.2
CYA 55

 

[mknauss]

SLAM is not the process.
Review Black Algae