I certainly lack the credentials of most of the folks on here, but I do have some experience with getting rid of it. I pro-actively attack algae problems instead of just sitting back and letting them slowly take over the tank.
First, get a good UV unit and you're off to a good start.
Aggressively run GFO and carbon. Cut down on lighting as much as possible.
Then take the rocks that are effected out of the tank and physically remove it by scrubbing them. The trick is not to stir things up in the tank by doing the work out of the tank, so scrub them, rinse and soak them in new water, then put them back.
This may require relocating things a bit but unless your down with months of trying to solve it, now is the time to do what it takes to remove it.
Sand too, suck it out of the tank and clean it out of the tank, do a section at a time right down to the bottom. Section by section.
Good luck!