From:
http://www.reefcleaners.org/index.php?option=com_content&task=view&id=54&Itemid=81
Gelidium, Red Wiry Turf Algae
Many species of short creeping red algae exist so the hobby generally lumps all of them under the heading "Gelidium", (the genus that is home to many of those species), and the common name Red Turf Algae, or Red Wiry Algae.
Manual Removal - Difficult. Macros that have fragile runners and creep along the rock are the hardest to manually remove. Do the best you can. Use a dental pick to do the most damage, DO NOT BRUSH. You will dislodge it and spread it. Yeah I know, it is boring as can be, but if you do it once surgically with a dental pick the problem goes away for good. If you can take the rock out, all the better.
Clean Up Crew- Emerald Crabs, urchins, sea hares, and large turbos.
Tip - Don't pass on frags with this stuff, don't put one in your tank. This algae has become extremely common on traded/aquacultured frags. So my advice is every time you add a coral or a rock look for it from now on.