If you have a REALLY bad problem, maybe consider doing a 3 blackout as per Tom's guidlines. Then, when your ready to unwrap the tank, make sure your dosing EI fully and have stable CO2.. thatll be as good as pretty much starting over.

Although a 4 day blackout didnt shift my BBA caused from my hit and miss DIY CO2 system. Now Im all stable again its certainly stopped getting any worse, soon Im hoping to see it back off a bit.

Might not be apropriate, but just a thought if you have a multitude of different types of algae.