Small Black Spots

[tfp_fan]

Today, I noticed small black spots in some areas of my plaster (please see the photos). I tested the water and here are the results:
FC = 1
pH = 8.2
TA = 80
CYA = 50
Based on the results, I know that the chlorine level is low and I need to add chlorine. I am wondering if the black spots are algea? Would you please give me some advice how to treat it? Do you recommend me to SLAM the pool? Is the SLAM target FC is 20 (I would like to know if the SLAM level is 20 in order to use my Pool Math app and calculate the required Bleach Chlorine to add to the pool).
Thank you.

 

[Rancho Cost-a-Lotta]

See if you can scrape up some of the black stuff with your fingernail. Wipe it on a piece of white paper. If it smears green, its most likely black algae:

Black Algae

This guide provides a step by step procedure for eliminating black algae in your concrete or gunite pool. Read full post here.

www.troublefreepool.com

DO an Overnight Chlorine Loss Test to determine if you have algae and need to follow the SLAM Process. Make sure you get your FC up to target level before the OCLT.

 

[tfp_fan]

See if you can scrape up some of the black stuff with your fingernail. Wipe it on a piece of white paper. If it smears green, its most likely black algae:

Black Algae

This guide provides a step by step procedure for eliminating black algae in your concrete or gunite pool. Read full post here.

www.troublefreepool.com

DO an Overnight Chlorine Loss Test to determine if you have algae and need to follow the SLAM Process. Make sure you get your FC up to target level before the OCLT.

Thank you. I followed your instruction, scraped up some of the black stuff with my fingernail, and wiped it on a piece of white paper. It did smeared green. I am wondering if I should go for SLAM process? or if it still needs me to do an overnight chlorine loss test to make sure?

 

[Rancho Cost-a-Lotta]

The treatment protocols for black algae and other forms of algae are different. I would do an OCLT first. If you pass, follow the black algae protocol. If you fail, follow the SLAM Process.

 

[JamesW]

I followed your instruction, scraped up some of the black stuff with my fingernail, and wiped it on a piece of white paper. It did smeared green.

Probably black algae.

It also looks like some copper stains.

What ever happened with this?

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We built our new pool last summer. It was in July that the plaster was complete. The day after plastering, the acid washing started late in the afternoon (due to the late arrival of the crew) and the job took until after the sunset when it got dark. After the pool was filled with water, I...

www.troublefreepool.com