Black Hair Algae (BHA).
Imbalance of carbon, low carbon levels.
CO2 injection and or Flourish EXCEL dosing will hold it back. There are a few critters that will eat it. Such as Siamese Algae Eaters (SAE). They will only help though not irradiate it. Most planted enthusiasts use at lest 1 of the above suggestions. I use all 3.