Maintaining 10 ppm FC at 20 ppm CYA should be fine for clearing the algae though Ben's chart says 12 ppm FC in the "shock" column, but you need to maintain that level so go a bit higher as needed (say, to 15 ppm FC in the morning, but not higher than that) and check it during the day (if possible). It sounds like the chlorine usage is declining so that is good.

I assume you are running the filter 24/7. Using a skimmer sock might help as well (will reduce how much backwashing you need to do). You are already vacuuming to waste so that's also good. There's just a lot to remove from your pool -- one way or the other.

Richard