I have been battling with the same algae, bryopsis, for a couple months now. Not an algae that the fish or even hermits will eat. Phosphates are likely the main fuel. Your LFS RO is probably the source. Test the TDS of the water if its over 5ppm its not good RO. I am having succses beating it with mannual removal and im running Grannular Ferric Oxcide (GFO) in a reactor. If the last few tough patches dont die off soon I will be using the Kent Tech M method. Plenty to read on this algae , GFO use and Tech M over on reefcentral. You need to move quick before this gets worse.