Dealing with black algae, what chlorine levels now from Best Guess Chart?

I started getting small signs of black algae at the beginning of last season but was bit sure what the small black dots on my liner were. Opening up this season its defiantly apparent what I have. Reading the forum posts on this problem, what chlorine level from "Ben's Best Guess* Guide to Swimming Pool Chlorine" do I need to shoot for. I am maintaining FC of 6ppm right now with my SWCG running at 100% for 10. hours a day. The black spots are not going anywhere but are not spreading. I have been scrubbing my liner for a week now and still lack about 30% to remove what's visible. I have lost about 20ppm over the last two seasons of Borates which I intend to replenish soon. I also will be raising my CYA to 60ppm as soon as I can get to a store that carries it. Closest pool store is over 40 miles away. My latest test numbers are: FC=6.0ppm, CC=0ppm, PH=7.6, Borates=30ppm,CYA =50ppm, TA=100ppm, CH=70ppm. Taylor K-1766 salt water test kit on order. Pool water sparklers and is supper clear!

Try shocking it up to about 15ppm and see if that helps. But, you cannot shock with your SWCG. Just turn it off for now and save your cell life and use bleach.