A little not so well known fact, emerald crabs do in fact eat bryposis. I hope no one ever contracts this horrible algae. It is probably one of the toughest algaes to beat in the hobby. I know many that have given up and just tolerate small amounts in their tank. We at Fragbox have had it before but because of the way our frag systems are designed its fairly easy to isolate and remove. When you get in your display tank however, it can be a daunting task to completely eliminate all traces.
This is what I have learned about bryopsis through experience.
It does not need a lot of light to grow but can also withstand great amounts of light. It can take over both high and low light spots of your aquarium. It is not specific to one area of the tank like diatoms or cyanos across the sand band. It can be found everywhere
It grows extremely fast. You can see it grow day by day. Its one of the faster growing nuisance algae out there.
It can thrive in low phosphate environments. Water changes and removal of phosphate via gfo or other methods will not rid this algae. These methods are useful against hair algae but you need different techniques to beat bryopsis.
Fish will not eat it. Tangs may pick it at here and there but generally they will not consume as it does not taste good. Most inverts will avoid it as well.
Manual removal does not help, it only makes it worse. By dislodging it and allowing some algae to float freely it will quickly find a new place in your aquarium to call home. Unlike hair algae, one of the worst things you can do is try to remove bryopsis manually. It almost always results in larger outbreak.
3 solutions to bryopsis that I found to work
If you can complete remove the infected rock or coral this is would be the best and would immediately solve your issues.
If its not possible you can try these methods
Raise magnesium with tech m to 1600-1700 for 4 weeks. I have tried it and it works. The bryposis turns white and then fall apart.
You need to keep mag high for 4 weeks and it only works with Tech M, Fish wont be affected, sps will lose some vibrancy but bounce back.
Finally the last solution I found to work are emerald crabs. They love the stuff. You need lots of them though. I mean LOTS
here is an example of a piece over taken by byrposis and how it was cleaned less than 24 hours later by emeralds