Oh yes, it's hair algae. Some is red, most is green. In some areas it grows as little tufts that are impossible to remove, while in other areas it grows in long, slimy strands and clogs up the filter intakes. It grows ridiculously fast.
I believe I have put 2+2 together on why this happened. The plants in my tank (several large Amazon Sword
, several Dwarf Swords, one HUGE crytocryne undulata, Cabomba, and a couple Hygro Kompacts) had grown so quickly I felt it necessary to do a serious pruning of them to give my fish some swimming room. I removed almost all of the Cabomba, the only fast growing plant, because it was driving me nuts. I also removed the Ozelot Sword
I had because I didn't like the way it looked with the rest of the plants.
I believe that gave the algae in the tank the opportunity to take over. Putting algae chips in the tank twice a week for the Corydoras probably hasn't helped either.
I'm going to see about finding some Hygrophilia or Rotala for the tank to replace the removed Cabomba with.