I'll look forward to someone answering this as I've got something similar to one type (the stringy but not rubbery one) only the color is more like a burgundy or deep purple-red. What is the red-grape looking one in the back of the first photo? I have a clump of that growing in my tank, too. Have no idea where it came from.
Could it be tubular thicket algae
? Described as "segments [that] profusely branch...forming dense hemispherical domes attached by a single holdfast. Segments are tubular, smooth, and relatively hard (heavily calcified) with flexible joints. Branch tips appear crosscut and have a central hole." Color is listed as reddish to orangish and off-white. [I love that SW identification relies on color terms like orangish!]
Edited by msscha, 03 April 2012 - 11:39 AM.