Steve,
I have this same red turf like nussiance algae growing all over my beautiful Marshall Island live rock.
I run a BB SPS dominated tank like you do & it's not a low nutrient problem. I also do not have high nutrients based on my last test with the following Salifert test kits. Ammonia, Nitrite were zero, Phosphates were undetectable, Nitrate was .02 ppm (less then a tenth), Calcium was at 440 ppm, Alkalinity was 9.3 DKH and PH ran 8.4 at peak and 8.1 at night. Those numbers are pretty good but the red turf algae started to take a foothold in June-July '05. My tank was setup in Feb '05. I did bi-monthly 20% water changes, tried Micro-Lift Special Blend Bacteria supplement, added 6 Mexican Turbos in August to the many Astrea & Ceriths that have been in the tank since day one. I really didn't see a difference. The red turf algae actually started to spread more. Two weeks ago, I added another 6 Mexican Turbos from FishTown (the first 6 were from Aquarium Adventure and looked a tiny bit different in shell pattern) and there seems to be a start of some progress or mowing now. I don't know if it has to do with the recent additions of the new turbos, or if it was also the 20 Trochus snails that I got from NEA at the frag swap, or the Special Blend Bacteria supplement kicking in or a combo of all.
Either way, it looks like it might be a slow process, but at least something or someone is starting to work.
cali_reef thinks it's from my use of Oceanic Salt, I tend to think it was off of some frag plugs when i bought a frag pack from Oceanrealm. I remember trying to scrub the plugs back then but it was difficult to get off without destroying the actual frags. Also remember some Carribean Astrea snails coming in covered with them also.
I spoke to JBNY about it & he didn't think that the Special Blend or Mexican turbos helped. He felt that the regular Astreas ate some of it but very slowly. I still say, try the authentic Mexican turbos.