I got worms in my tank now.
The tank has got water in it, but no fish and the water has just been sitting. I've now got cyclops and weird worms. Are they deadly to fish? I meant to empty the tank and clean it, but I haven't had the time, now there are worms hanging at the surface of water; they don't swim.

My questions:

  1. Are they harmful to fish?
  2. How to clean tank and get rid of them and cyclops?
  • 3
    you need to give more information how do the "worms" look and behave,where do you live. Mar 24, 2018 at 5:35
  • 4
    If you're having a hard time describing them, take a picture.
    – Mario
    Mar 24, 2018 at 6:47
  • 3
    As Mario has mentioned, take a photo! They are wonderful additions to a question :) Mar 24, 2018 at 11:14

2 Answers 2


I might be wrong on this, but it sounds to me like you have got mosquito larvae in your tank; if this is the case, they provide excellent food for any fish.

If they are mosquito larvae, they will rapidly swim down from the surface of the water if you disturb the water. They inhale air with a siphon placed next to their anus, so they are hanging head down from the surface.

If this is the wrong type, you have to give more details in your question for me to solve it.

You clean the tank as normal and vacuum the gravel and clean the pump and filter.

Cyclops are fishfood, so your fish will remove them, it will probably be a lot of living things in the gravel your fish will eat this too.

Parasites need fish and die without them, so this is normally not a problem when you restart your tank after it has been unused for some time.

Remember: before you add new fish to your tank you need to cycle it, this is to build a healthy bacterial flora to handle the waste from your fish and food.

You can read how this is done in this article; pet stores do often not inform you about this, but it is very important to know if you want to keep the fish alive.


They're more than likely free swimming nematodes. White and brown'ish ones are very common in most fish tanks. You'll see them on the glass or swimming. They are typically readily eaten by fish.

It's highly unlikely they will be a threat to any fish. Almost no fish parasites are ever visible in the tank even if they have a phase where they aren't attached to a fish such as freshwater ich.

Also, do not completely empty the tank, ever! Do routine smaller water changes and make sure to use a tap water treatment to remove chlorine and chloramines. Most pests like these will go away on their own with a healthy tank.

  • 1
    Dam I keep forgetting to not press the 'return ' button on my phone and post things right in the middle of a comment lol- Any way I'm not planning on using that particular tank( with worms) so I emptied most of it, cause I needed the space for my fry grow out tank.. should I bother boiling all the gravel ect? Or not really since the cyclops and worms aren't harmful to fish? Or how should I sterilise the tank for next time I set it up and cycle it? Thanks
    – user10731
    Mar 27, 2018 at 21:50
  • 1
    I would either let it dry out completely and do nothing after that. Or if you really feel the need to actually sterilize it, I would use 1:10 plain bleach and water, then drain and let it completely dry. Bleach is a lot safer than most any other cleaning method and if there is any remaining liquid, you can use a tap water treatment to neutralize it when you refill. Do not use scented or anything but plain bleach.
    – Jestep
    Mar 28, 2018 at 20:27

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