Yep, red bubble algae. Got it in my sump. Grows slow enough, it gets bright red dots on the bubbles when they get large.
http://www.reefcleaners.org/index.php?option=com_content&view=article&id=54&Itemid=60
Red Bubble Algae, Botryocladia
Red Bubble Algae is one of the Botryocladia species, (probably skottsbergeii or pyriformis) . Some of the Botryocladia species, like Botryocladia occidentalis, are desirable. The main difference between an invasive species of Botryocladia and a desirable one is how it grows. Desirable species grow up from branches, and invasive species creep along the rock just leaving hard to remove bubbles. Some are in between both in risk and branch development.
Manual Removal - Don't be clumsy and spread this one. Get em small, cover them with a baster, scrape the baster along the rock, when the bubble comes off release the plunger and suck it up. Discard and repeat. If you have a lot to do, by the time you are done you will be ready to add new mixed water to complete the water change. Be aggressive with your manual removal.
Clean Up Crew- Emerald and Ruby Mithrax Crabs will eat it, as well some Rabbitfish. Juvenile Mithrax are generally best for the task, the smaller the better.