This morning I have found a lot of small white worms hanging around the walls of my fish tank. Do you know what it is? It might be a planaria, but I am not sure. Should I be concerned? planaria

  • Can you post more pictures? It's hard to tell by the photo, but it would suggest it is some type of flatworm, there's many different types other than planaria though. Also is this freshwater or saltwater?
    – Jestep
    Commented Dec 16, 2021 at 17:05
  • OK, I'll post more pictures tonight. I'll try to not smash the worm too much, as unfortunately happened to the one in the picture :). To answer your other question: this is a freshwater tank.
    – Alexis
    Commented Dec 17, 2021 at 18:41
  • Did you ever get to take more pictures? Commented Jan 9, 2022 at 22:52
  • Two days after taking the above picture, I left for vacation. Searching on internet I have found that over-feeding might have been the problem. Therefore I reprogrammed the automatic feeder to run twice a day instead of three times, while I was away. When I went back from my vacation, the worms were gone. Anyway, thank you @MikeCiffone for your very detailed answer below.
    – Alexis
    Commented Jan 11, 2022 at 18:33
  • Maybe of interest too: What is this alien in my shrimp tank? Commented Jun 11, 2022 at 4:04

1 Answer 1


I don't know of any "good" worms.

If you've got worms in your tank it's a sign of over-feeding or inadequate filtration. So figuring out the cause is key to keeping them from coming back.

This particular specimen looks flat and rusty colored to me, which would be indicative of the "bad" kind of Planaria. Detritus worms would be long and skinny.

The easiest thing you can do, albeit the most extreme measure, is to treat the tank with Fenbendazole.

Fendebdazole, commonly sold as Panacur C (a dog de-wormer) will send Planaria into oblivion within 2-4 days.

Panacur C (Fendebdazole) Dosage for Aquariums

You'll need 0.1 grams per 10 gallons.

Be sure to remove any carbon or chemical media, as well as any snails if you have any (and want to keep them).

If you're having trouble with the measurement (requires a kitchen scale), you can take a 1 gram packet and dissolve it in a 500 ml of dechlorinated tap water or tank water. In this case you'll dose 50 ml per 10 gallons.

Re-dose after 48 hours. Then wait another 24-48 hours (You'll know when they're dead).

Follow this up with a massive water change (~80%) using a gravel vac to pick up the casualties and add a carbon to your filter and let it suck up any remaining meds. Remove it or replace it after 24-48 hours.

I always wear nitrile gloves and a mask when handling any medications.

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