If and when your pool is fully clear and clean, you should start adding Polyquat 60% as a preventative. You could add about 1/2 quart to start, then add 2oz every week and that should inhibit the black algae getting started again. Polyquat is easily recognizable by the contents: 60% poly...(something unpronounceable).... as the active ingredient. If you see something else and you DON'T see this, it ain't Polyquat 60%. Sometimes it's labled as algaecide, sometimes as Mustard Algaecide, sometimes as black algaecide. I don't care what they call it as long as it's got the 60% poly......

Then you may be able to lower the FC safely. Beware, though: A heavy dose of Polyquat--like a half quart to a quart--will cause your FC to drop like a stone over the next 24-48 hours. Don't worry--with the SWG or shocking it will come back up. Just don't back wash for a couple of days.

And the Poly acts as floc treatment, too.

Good luck!