Black Algae Killed by pucks

[CTIGuy]

We have a 45K gallon Gunite Pool and thanks to this website and the test kit I have had an easy time keeping it clear and algae free for the past year. My pool is also a salt pool with a CL generator that runs at 100% (CL generator is undersized) for the 10-12 hours the filter pump runs and I still have to add bleach to keep it at the 1-3PPM CL suggested by the Mfg. Someone suggested I try adding more CYA as the Mfg suggests 50-75 PPM and I was at CYA 20 PPM and keeping the FC at 2 PPM. The CYA mfg suggested adding half of what was needed 1 day and the other half the next. With such a big pool I needed quite a bit of CYA so I added 1/3 the first day and another 1/3 the next. After a few days I noticed white crust lines on the walls near the sheer decent into the Spas and the spas tiles under the sheer decent were etched white. I assume this was the CYA but not sure so I asked the pool store and they said no way. My CYA now at 40 and not sure I want to add more and do more damage.

My other numbers
PH 7.6 (needs a lot of ACID to keep it there)
Alk 80
Cal 360

A few days after adding the CYA I started to see dark streaks on the bottom of the pool. Brushing did nothing except you could see a bit of a cloud coming off for a few strokes, I assumed I had been hit by the dreaded black algae.

Based on the advice read here I shocked (above 15 PPM), brushed and vacuumed 2-3x per day my pool for a week and it did nothing to the black algae. I brushed really hard on the algae areas but it seemed to help spread the algae. I had given up on the shock method and was going to wait till my kids go to camp in 2 weeks and try a “wet acid wash” on my Diamond Brite finish in hopes of bringing back the Midnight Blue color and getting rid of the black Algae.

Yesterday a neighbor asked me if I wanted his tri chlor tabs as he had the high Cya problems and has decided not to use them any longer. I had read here others had rubbed them on alga and it worked, so I took 2 and tried rubbing it on the streaks of black algae. After the rubbing and after playing with the kids in the pool for about an hour I noticed the streaks fading but it was dusk so I was not sure. This morning the algae is gone in the areas were I rubbed the pucks. I did not get the deep end very well as my puck was getting small and my kids wanted to play.

Lots of CL and brushing did nothing. I am sold on the pucks for black algae.