asparagopsis taxiformis?
http://www.aquatouch.com/algae.htm
If that's what it is, then I've read a lot about people with bare bottom low nutrient sps tanks that were plagued with the stuff. It was taking over my rocks, and a combination of manual removal and Mexican turbo snails pretty much eradicated it. Not in the article that it has 2 distinct stages of life that look completely different.
Good luck
Myles