Black algae … I think

[Colbuster]

Hi.
I’ve been working hard to get my levels perfect with an in ground plaster pool with SWG, but I have small little dark spots on my plaster. The water is crystal clear.

CYA 55-60
pH 7.2-7.8 (treating for 7.2 every time)
FC was 9
CC 0.5-1.0
TA 90

Most of the spots are the size of a bean except 3 that are dime and quarter size. I took wire brushes to all the spots and they barely change. The big ones change a little more but not matter how hard I scrub I can’t completely get them off. Anyway - I am slamming now per the recommended levels on the forum and pool math.

1) Will those spots go away on their own if this slamming process works? I read that they have a little cap that protects them. What else can or should I do?

I’m treating to get my FC level at 23. I’m 16 hours into the process. Lost FC overnight, which I expected. Levels are back up again as I added more chlorine.

2) If I don’t lose any FC tonight (OCLT) am I done?

Thanks in advance!

 

[duraleigh]

Since you started the SLAM process, go ahead and complete it. You are finished with the SLAM when........

1. Your Pool water is crystal clear with no visible sign of algae
2. You passed the OCLT losing not more than 1 ppm of FC
3. Your CC's test is either .5 ppm or 0 ppm.

Will that make the black spots go away? Probably not right away. Do you have a pic?

 

[Colbuster]

Since you started the SLAM process, go ahead and complete it. You are finished with the SLAM when........

1. Your Pool water is crystal clear with no visible sign of algae
2. You passed the OCLT losing not more than 1 ppm of FC
3. Your CC's test is either .5 ppm or 0 ppm.

Will that make the black spots go away? Probably not right away. Do you have a pic?

It’s in my deep end. So I don’t have a way to get a good photo. It’s greenish black and feels smoother than the adjacent plaster. I’ll try a photo.

 

[Colbuster]

Since you started the SLAM process, go ahead and complete it. You are finished with the SLAM when........

1. Your Pool water is crystal clear with no visible sign of algae
2. You passed the OCLT losing not more than 1 ppm of FC
3. Your CC's test is either .5 ppm or 0 ppm.

Will that make the black spots go away? Probably not right away. Do you have a pic?

 

[Colbuster]

We had one before when I was paying a different company to “maintain” my pool and he said it was algae. I’m not sure how they got rid of it at the time.

 

[JamesW]

Black algae is a type of bacteria.

If it is black algae, then you should be able to scrape some off for examination.

The bacteria is toxic in large amounts so be careful with any samples.

 

[Colbuster]

I just checked my FC and it’s at 26. So I hope that is killing everything. I’ll run check the OCLT tonight too.