OK apart from the tiny microscopic white worms I had in the water few days after setting up the tank, which I was advised here that they are not harmful and they can form a good snack for my Mollies but now strangely there are black/dark gray worms, they are like 3-5 mm in length and 0.2-0.3 mm in diameter, clearly visible little bastards, I can resemble them to the fly worms except for the color, they are on the glass just above the water line so they are not swimming in the water like the white ones but keeping themselves wet, what are these?!! Are they harmful?!!