I had a similar problem a few months ago, and once I got serious about fixing it, it didn't take much.
Here's what I did:
Beefed up my cleaning crew
Replaced my or membrane
Added a brs gfo reactor
Then I did 50% water change and picked as much algae off the rocks and glass as possible.
The algae that was left turned brown so I did another water change and it came off really easily. After that The algae hasn't come back.