Loverotties said:
The one thing with nudibranch is that they don't live that long .ussally 6 months.
Rottie's hit on the reason I was hesitant to answer.
I don't know a lot about Nudi's, other than the fact that they don't really do well in aquariums. From what I understand, marine biologists don't know a lot about these guys either. More importantly, what they eat. In even an established tank, they seem to last about 6 months. Research suggests that this is about how long it takes them to starve to death.
I've also heard that due to the fact that they have NO skeletal structure and quite flexible internal ?organs?, they are capable of bending/sliding/oozing into some very tight spots, and are well known for getting into PH/pumps/overflows/plumbing/etc.
So while I don't know a whole lot, what I DO know leads me to suggest NOT getting a nudi.
I was more on-board with the Lawnmower blenny idea...as he's done wonder's for my tank's algae. Maybe ask your LFS if they can get you a smaller one. Or let you just *BORROW* a bigger one. Let him chomp away, and take him back when all's well.
The best answer to this question, may not be one you want to hear, but is best for the tank. You need to do whatever you have to do to determine the SOURCE of the hair algae. I'd do a search on here for "Hair Algae". you'll find TONS of threads...all with the same advice repeated (in detail). Hair algae is either caused by a lack of nutrient exporting, or by adding rock that came from a system that had a lack of nutrient exporting.
Getting ANY critter to eat it now, is just putting a band-aid on the problem. And in few weeks/months, you'll have the same outbreak again.
Sorry I didn't respond when I first saw this, but didn't really want to jump on the "Don't Buy critter X" band-wagon. General rules that apply to a specific critter, may not apply in ALL cases.
Anyways...hope this helps, and if you have more questions, please fire away!