Looks kinda like this from Reefcleaners.org:
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 remove it if possible. Fragments of the algae can spread though, so make sure to net any pieces that break loose. 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.
Tip - Don't pass on frags with this stuff to other hobbyists, 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. It is easier to keep out of the tank then deal with it once inside.
Clean Up Crew- Emerald Crabs, urchins, sea hares, and large turbos.
