That is definitely cyanobacteria starting and it can be in the substrate along the glass edges of the tank as well.
The best and most efficient way to get rid of it is to do a 5 day treatment of Erythromycin. Many people use Maracyn but any fish Erythromycin will work. It won't harm BB and the only thing that can happen is that you get a slight ammonia spike due to the dying bacteria in the water. It's best to manually remove as much of the cyano before treating as possible.