Matt,
I have been fighting bryopsis plumera since October! This is not your ordinary hair algae...it thrives even in low phosphate tanks. I thought it was some sort of delicate macro with soft, bluish green fronds. When it spread to another rock, I started tweezing it out and it spread like wildfire throughout my 135. I added a GFO reactor in December and it hasn't slowed down.
The rocks that I can remove, are scrubbed and dipped in peroxide for 3-5 minutes, then rinsed and placed back in. I have gone through almost a gallon of Tech M so far and the bryopsis doesn't appear to be melting away like some say theirs do. If you go the Tech M route, please be sure to test for magnesium and try and keep it in the 1600-1800 range for about two weeks. I'm shooting for longer and hopefully this will not kill my shrimp, snails, rbtas, etc. in the process. So far the sps and most of the softies are doing fine.
It sounds like it may not have spread deep within your rock...thank goodness for that! Nip it in the bud, now! Good luck!