I had some BBA show up in my tank a few weeks ago when my CO2 ran out -- probably not as out of control as yours, but putting some nerites and otos in the tank seemed to help some. I'm not sure if they always eat BBA, but these guys from the LFS seemed hungry. The leaves that weren't completely infested actually got pretty clean over about a week and I just trimmed off the really nasty ones. Adding CO2 back seemed to make the problem more or less go away. Good luck!