Is this a filmy brown algae? If so it is likely diatoms and they are almost always present in a newly established aquarium. As your system ages they should go away. Even if nutrient levels are high, the diatoms will likely go away and be replaced by something much more annoying. Keep your nitrates low and try to get those phosphates to zero and you should be set. Diatoms also rely on silica to make their frustule (cell wall) so if they don't go away, you can try a silica removing media.
HTH & GL,
Kevin