I've been getting black algae in the corner of my pool for a while now. it started in '08 when I left on my honeymoon for 2 weeks, returned and the algae had set in. I poured bleach in that area and left the pump off over night, having used a metal brush prior to bleach to "pop open the cells". it seemed to have worked but they came back (same corner), and slowly started to spread. went a step further and poured cal-hypo (65%) all over the areas of affect (stairs, that corner, and some further out) and again brushed first left pool off for 12-18 hours, seemed to have worked again until a couple months passed and it was back in that corner. I'm sure its because I get poor circulation back there so firstly I need help directing jets for perfect flow of water.
I have attached a picture of my pool, blue dots represent jets, blue arrow is direction previous owner/pool guy directed them, yellow is my pool light, purple is my quick disconnect for APC, red are suction lines (main drain + skimmer), and the big black heap in the top right corner is the black algae colony origin.
I will be adding borates as my pool vendor (runs servic company, I trust him as he uses Taylor kit for testing and respects BBB method) suggested it to help fight off the black algae, he had a friend with a similar problem that was resolved by adding 50ppm borates.