i have had my share of this,
sparing us having to read other posts to keep up with your new tank,
it would be better on each post if you post the pertinent info. sorry
about that, you may have posted this info already, i dont feel like
scrubbing the posts to find out. :-)

what type of lights do you have? i forgot, but may hav easked
already. are they NO's?

it may be the phosphates currently. can you buy a bunch of turbos?
its not unheard of to buy 1 snail per gallon of water, and hermits to
MINIMAL cleaning of GHA. since its on teh glass, a few good mow downs
from snails may be your best bet while you starve your nutrients which
can be a slow process. bristle worms, or may be a different species,
will decimate that hair algae if you keep it unstirred. let them lay
their eggs on it, and they will chop it all at the roots, but that is
a few week process and will get real ugly. then a slime coat covers
it and starves it. if you see the slime coat growing over, dont
disturb it, cause its almost gone, but took me weeks for that to
happen once. of course thats when i was using OLD NO's. hopefully
you wont have to go that route.