This is the first thread I've noticed where this algae has been brought up. I thought I was alone (and was so depressed about the condition of my tank I didn't even want to photograph it.
At this point I'm losing zoanthid colonies, GSP colonies, monti caps and a couple of branching SPS to this plague and my plan currently involves a teardown and scrubbings with more 'control' grazers in the new smaller tank. When I first noticed this algae I had just gotten rid of my last Turbo (it was a bulldozer and this could have come in after the Turbo was gone anyway). I've been using manual removal and siphoning for the past couple months and have also added a Diadema urchin (which has only eaten this stuff by accident while chasing coralline algae). The siphon works well and the infested colonies seem to return to life with vigor for a few days after the harvesting, but the red fuzz just grows to fast for me to keep up with it.
I think the worst part for me is that I was excited the first time I saw this algae. It is pretty in small amounts. By the time I saw it as a problem-algae it was too late and I was fighting it, bryopsis and the brown-irredescent-super-thin algae that I think starts with a "D" but I can never remember. Beat the "D" algae nearly completely, made good headway with the bryopsis for a time, but the red just doesn't give up.
I don't remember now if this was mentioned above, but Magnesium dosing has been suggested to me locally as a control by someone else who has had this algae in small amounts.
My tank is only a 75g and it's breaking my heart, can't imagine a 750 being overrun with this stuff... it's just too much.
From my tank in August:
From my tank (same area) in December"
Another area - formerly zoanthids:
Good luck in your battle.