Is this algae?

[WWells]

I came home from out of town a couple of weeks ago and there was a light dusting on one of our steps and a string on a ledge, similar to picture I took today. This ledge keeps getting a spot that starts small, in the same place and grows across the leading edge. I brush it and it comes back over a couple of days. I did do an OCLT 3.5 evening, 3.5 morning with pump off overnight, was I supposed to have it on with SWG off? It’s been so many years since I learned the TFP way I haven’t had to treat algae bloom in 13 years and have taught many the way to the promise land. This summer with the heat, sun, rain and my travel I may have errored

TF-100 test yesterday evening
FC 2.5
CC .5
TC 3
PH 7.8
CYA 40
ALK 70
Salt 3200

I added 128 of 10% and 20 oz of dry stabilizer since

Should I SLAM or do an OCLT tonight?

thank you

 

[PoolStored]

Looks like algae, but might be dirt. For the price of an OCLT to avoid the SLAM...do the OCLT.