This is a stupid thing to ask, maybe, but how is your water testing?
I have just recently completed about a 50% water change, over the course of a week or so, because I wanted to start adding some coral to my FOWLR
(my water quality was not always the best, and I kenw that I would need to make it better, for the coral to survive).
Now, the water tests great, and the first thing that I have noticed is that my coralline algae (white and purple) is growing like crazy. Seriously, in a week or so, it has spread from 2 pieces of live rock to all of the live rock, more-or-less equally distributed around the tank.
Again, I recognize that this is probably stupid. But it's a recent triumph for me, so I figured I'd mention it. Maybe try a substantial, but gradual, water change, and see if it improves the water quality any. Might help...