Reply To: Small, thin worms in breeding tank. Welcome to the website! › Forums › General › General Aquaria › Small, thin worms in breeding tank. › Reply To: Small, thin worms in breeding tank. May 30, 2007 at 11:53 am #11259 JimboParticipant I’m guessing it’s planeria. Nothing to worry about. Just cut down on feeding. Here is a really bad link: http://yucky.discovery.com/noflash/worm/pg000220.html