tiny worms in my aquarium

Question
Hey I have a 42 gallon freshwater aquarium with 4 red belly piranhas in it. Over the past few days I've noticed that there are tiny worms that are a really pale green and almost look white that are crawling around on the inside of my aquarium. The worms are about 2 to 3 millimeters long and have a diameter of about like a piece of pencil lead for a mechanical pencil. If you could help that would be awesome! Thanks

Answer
Riley,

 It sounds like you have planaria. These are little worms that come from uneaten food in the tank. It will not hurt the fish and you might even see them eating the worms. I would do a water change and vacuum the gravel. Also, to keep them away try not to over feed your fish. Only give them what they can eat in 1 to 2 minutes, removing what they don't eat.