I just happened to have stumbled on this over at RC, and thought that it might be something that would interest a few people.
The link details one guy's battle with bryopsis and how raising his magnesium levels to around 1600ppm seemed to cause it to die off while minimally impacting the rest of his system.
Reef Central thread: Finally an easy solution to byopsis
The tail end of the tread does discuss how this works and doesn't work for some individuals. There is debate about people wrongfully identifying their algae outbreak. There is also further discussion about what type of bryopsis may/may not be affected.