+1 to Ryanj's recommendations.
Try testing for phosphates in the morning while the room is still dark. I understand this is the best time as the algae should be more at rest.
And if you have a few bucks, or know someone with one, get your hands on a Silicate test kit.
I bought one for $14 to rule it out.
If the your phosphates are really hi, maybe cut down on your food some.
This is an example of a good way to deal with phos
http://www.jlaquatics.com/phpstore/s..._ID=tf-reactor
I've been told the best media to use in it is HC (hi capacity) GFO (granulated ferric oxide).
2 places I know to get it from are CACO3REEF and Bulkreefsupply.
Not the crappy pellets, but this stuff
http://caco3reef.com/gfo/gfo