What is a threadlike worm in my aquarium?

Answer by  Tank (539)

Depending on whether you have a freshwater or saltwater aquarium it can be a few options. In a saltwater tank it is most likely a bristle worm. For a freshwater tank it is probably a planaria worm. They are found because there is too much uneaten foods in the gravel. Siphon the gravel and the worms will leave too.

Answer by  meridian (466)

The thin worm that you are seeing in your aquarium is Planaria. It won't hurt the fish, but because they eat waste and food that the fish don't eat, their presence is alerting you that you may be feeding your fish too much. Feed them once a day, an amount they should be eating completely in 5 minutes.