I think out of all algaes, peroxide wont work on BGA. Instead use erythromycinTake a turkey baster and some hydrogen peroxide. Squirt the H2O2 directly on the BGA; this should kill most of it. Repeat as necessary; the dead growth should peel away easily after a day or two.
Since bga is a bacterium, the erythro kills it. Though some are a bit more cautious with erythro since if you use 2 much it may kill off some of the benefitial bacteria as well.It's worked for me in the past, though it takes more applications than for green algae. I've never tried erythromycin.