It doesn't look that bad right now, to be honest. You can probably control the growth by pulling out what you can, and using something like macroalgae to help control phosphates/nitrates in the tank. If you like chemical methods, GFO does a pretty good job of combating the issue.
If you get a large patch growing in your tank, you can try Kent Tech-M. Do a search for how to dose it for bryopsis. I'm sure there are better directions then I can give off the top of my head...