FYI..
I started a new tank as well, got some live rock with decent corraline coverage, 110 watts of PC lighting on a 29 gallon
(1 55w actinic and a 55w 10k).
I have kept Ca, Alk, SG as close to currently accepted parameters as possible, PO4, NO3 have been coming into check as well with time.. (using DI water and dripping Kalk) doing a 10% water change every 2-3 weeks or so..
After about 2 months I started seeing obvious spreading of corraline on the rocks. (Look for the bright white, verrry thin edge on a patch of corraline)
It has been exactly 12 weeks now, and I have many pea-size purple circles growing on my back glass and plastic tubes... It seems to like the plastic surfaces best..
As has been stated before, it seems to spread faster over the glass and plastic than the rocks, but hey.. you cant have everything..