My blue leg hermits from Reef Cleaners pick away at that quite a bit. I'd see if your CUC can help with manual removal, worst case scenario I used Flux RX on some Bryopsis I had and it crushed the algae in the tank.
best thing to do is try and eliminate the source. Do you perform weekly or bi-weekly water changes? What is your PO4 and NO3 currently at?
Do you feed heavily? frozen foods can have a lot of PO4.