The dreaded Black Algae

[Mutley]

I recently moved into a house with 33k in-ground gunite / plaster pool. Pool is ~15 years old and still original plaster that's probably will need replacing soon. The house was vacant for close to 1 year and the pool maintenance wasn't really kept up. After fixing broken equipment and following directions from local pool supply store, I have the water very clean. There now looks to be black algae in all the areas where the plaster is thing or rough. So after reading up on everything here, I started the SLAM process 3 days ago. It's a SWG pool, so I have been using 28 to 31ppm as my FC level. After 24 hours my FC and TC levels were the same, and the last two nights FC has stayed the same. I have been brushing twice a day with stainless brush but the Algae is not getting any less.
So my question is should I keep the pool at SLAM FC levels for more time, Should I let the FC level fall to normal level, or should I let the FC fall to an elevated FC level (~10) and hold it there for more time.

Before I started.
CYA 75
Ph 7.2 <- Was 7.8 but lowered it before starting SLAM
FC been keeping to between 28 and 31

Thanks for any input.

 

[Mr Bruce]

You may have seen it already, but here is the black algae article Pool School - Black Algae

 

[Mutley]

Thanks for your quick reply. I had read that last week, but had actually overlooked / forgotten about it, with all the other information I had read. So if I understand that article correctly, it's stating that now my SLAM process is complete (passed FC over night test & CC is 0), I should let my FC drop to the high end of normal (6ppm for me), and keep it there and keep brushing until the algae has gone?

 

[Mr Bruce]

The way I understand the article is to keep it between target and SLAM. So in your case, I'd shoot for around 10 or so at least. The main takeaways from the article are lots of brushing, rubbing pucks on the algae if brushing alone doesn't do it, and make sure there aren't any hidey-holes for algae. Good luck

 

[pooldv]

Agreed, keep FC at about 50% of shock level.

It is safe to swim with FC between minimum and shock level for your CYA, [FC/CYA][/FC/CYA]