It's a species of Botryocladia (a red bubble algae), it will normally die off by itself in nutrient poor tanks. You can manually remove the stems and bubbles carefully by hand without popping the bulb and releasing it's spores as the bubbles are not that fragile until fully grown.
Personally I've always liked the look of the stuff.
Thanks for the info David. I have been picking it off of the rocks, trying not to burst any of the bubbles. I will continue to harvest it to keep it under control.
