I'm going through the same thing right now, I used all dry rock with a few little pieces of live rock for seeding. The way I am attacking this thing is by simple water changes, gfo and gac changed every two weeks. I should bump it to once a week but I cant afford that much salt. It took over every piece of rock in my display, I have been battling it for about a month now. Its been really up and down, it would start to recede then come back but lately I've been winning this battle, in patches its been turning brown and then white and dying off. I test Po4 W hanna and No3 with redseapro and salifert test kits, everything is at zero but unlikely due to the presence of algae.