I ain't the expert, but kept my FC level in the upper teens to low twenties for over a week to get rid of my algae problem. To the point where I started to see the liner begin to fade at the seams. I brushed and backwashed every day and also got into the pool and hand rubbed the underwater hardware (steps, ladders, hidden places). Checked my phosphates regularly too.

The mistakes I was making in the past was thinking that you could get rid of algae with a bottle of "stuff" and a vac to waste. Now, after doing my research here, I discovered it's a "process" of staying with it for a couple of weeks to get rid of.