I had a similar problem in the past, only the infestation was in my oscar tank and he had no interest in nibbling the white worms. I believe the worms in my tank were a type of Planaria, and it was easily remedied by keeping the tank cleaner. They live on the waste in the tank, and when there isn't enough - the population quickly dies off. As far as I can tell by web research, the worms aren't harmful to fish - some people actually culture them for live food. Hope this helps.