Sorry, but green algae isn't caused by overfeeding. However, it doesn't help. Overfeeding causes a flimsy algae that is easily removed.

You must be getting light from somewhere. You shouldn't have that much trouble from artificial light. Do you ever leave your window open, letting light into the room.

An oto should clean up the problem, and prevent any algae in the future. They stay small, so you should have a problem with being overstocked.