Pool opening surprise--is this a new kind of red algae?

[Maria]

Been opening my pool for years with knowledge from this site, so green slime or water doesn't phase me.
But what in the heck is this? Do I just continue with my normal pool opening procedure? It continues around the water edge along with the normal green algae...

 

[Richard320]

Can you scoop it up and feel it? It looks like it might be dust off the coping.

 

[Maria]

No, it's definitely growing. It's all around the scum line of the pool also. Bricks are not new, although the stuff is brick colored.
I just need to know if I should use a higher SLAM number if it's some sort of weird algae.

 

[pooldv]

I used to get red algae in my saltwater reef tanks sometimes. I would start with a regular SLAM. If you pass the 3 criteria amd it is still present then try mustard shock 24 hour treatment.

 

[Maria]

Ok, in process of SLAMing. Balanced pH to 7.2, then Alkalinity to 110. Brought chlorine to 14 just in case it's a harder to kill algae than green. Have backwashed twice. Brushed twice. Chlorine dropped to 13 in 3 hours.
Aaaand, the red scum is now turned black. Fading, but really hard to scrub off of the waterline.

Do I treat it as black algae now that it has changed from brick red to black? Green water changing to blue.