Possible Black Algae?

[adam_d]

I've been battling a few black spots in the pool for a couple of years now. I've had the pool 2 years, not really getting serious about maintaining until this year. Pictures will show a few spots of what I believe it black algae. In the first months of the season, I kept FC at SLAM level, and with heavy brushing for several days, the marks do not seem to budge, I'm hoping its just a case of impatience. The past couple years, the chemistry was neglected during the winter months (didn't have a tarp and was allowed to get very dirty prior to closing.) Just wanted the opinion of this being BA or some sort of staining/scratches in the plaster? The spots are not slimey, most of them just feel rough to the touch.

Current levels w/ a TF-100 kit.

FC - 4
CC - 0.5
TA - 70 (a bit low)
CH - 250
CYA - ~15 (when doing the test, the dot gets NEARLY unvisible around 20, still working on getting this up but daily FC depletion seem to be under control)

Any information would be appreciated. Thanks all!

Dropbox - Photo Jun 30, 11 35 14.jpg
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Dropbox - Photo Jun 30, 11 35 56.jpg
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Dropbox - Photo Jun 30, 11 36 16.jpg

 

[pooldv]

Have you read this article from Pool School?
Pool School - Black Algae

 

[adam_d]

I have. I've never had fertilizer near where the spots are. As for the "small dark aggregate particles", this sounds like my situation except its on the wall. I don't think a non-slip surface would be applied here. I've taken a trichlor puck to the areas and it has had no effect on them.

I've read some cases to where the BA has been so bad, it needs to be chipped out? But then contradictory statements stating that high FC and brushing will do the trick.

 

[adam_d]

I guess my question is, is there anything that could explain this besides being black algae?