| Since it is hard to get a picture of things that small, do a few google searches for planaria in aquariums and see if those pics resemble what you are looking at. From your description, that is what it sounds like. Planaria aren't directly harmful to fish (in fact, some will eat them), but are usually a sign of overfeeding. I say "usually" because I have now seen them twice, both about 2 weeks into new tanks, in which I was certain I wasn't overfeeding. When you find planaria, decrease your feeding somewhat, and be more careful about gravel vacs. When their food source is reduced, their population will reduce.
*edit* Shawnie beat me to the punch! |