help out an old newbie

I'm a newbe here but I've been a pool owner for about 13 years and have had the same pool in my family for a total of 35 years (I bought my parents home). I have a big black algae problem... first time this has happened I know why,, I goofed on the chems in the spring and heated the water.. then to top it off we had a major storm blow in and the power was off for the last 5 days...I also have alot of very large oak trees that are close to the pool and you quessed it a full trash can of leaves and sticks at the bottom I've read all the back post that I could find on black algae,, because of cost and time I'm just going to drain it.... I have the help and the equipment... some specs: 20X40 12ft deep 48000 gal,, concrete. My question is what chem or acid should I use to scrub it with. I want to make sure I kill all the spores... the paint we have used for all these years is a latex based BONDEX brand pool paint.. It's paint mixed with portland cement... It's a very rough finish ...... thanks for your help
marvin