What Are The Tiny Black Worms In My Fish Tank? {Are They Harmful?}

It’s tank maintenance time and I’m staring at something I never saw before. What are the tiny black worms in my fish tank?

If you see tiny black worms in your fish tank you will need to take action right away. Get rid of them before they do harm to your fish.

This article will highlight, explain and give tips on eradicating black worms and other unwanted guests in your tank.

What Are The Tiny Black Worms In My Fish Tank?

There are four types of little black worms we need to be worried about in the fish tank, they are:

  • Detritus Worms
  • Planaria
  • Anchor Worms
  • Camallanus Worms

If you find the above worms in your tank you will need to change 50% of your tank’s water then treat the water with a aquarium parasite treatment kit which you can buy on amazon.

The treatment might be different depending what work is in your tank, I will go through the treatments below.

What Are The Little Black Worms In My Fish Tank?

The most common black worms in your fish tank are Detritus worms, Anchor Worms, planaria or Camallanus Worms. You can determine this by studying the appearance of the tiny black worms in your fish tank.

Below is how you can identify what type of worm is in your tank

1. Detritus Worms

Detritus Worms are commonly found in your tanks pebbles and your substrate, they look like thin, pointy, white-brown strings that wiggle through the water.

Below is a video which shows you what these worms look like.

YouTube video

2. Planaria

Planaria are the most common black worms in your fish tank. Planaria are a type of flatworm.  These worms have flat worm-like bodies, and paired eyespots (ocelli) that give the appearance of being cross-eye.  Below is what these small black worms look like.

YouTube video

3. Anchor Worms

Anchor worms are the most dangerous worms you can have in your tank.  These worms will attach themselves to your fish. They are external copepod parasites that are tiny and are just about visible to the naked eye.

4. Camallanus Worms

Camallanus Worms are another type of worm that is common in fish tanks. Camallanus worms are a couple of millimeters long when fully grown and are usually found in the anus of your fish. In the video below you can see a Camallanus Worm attached to a poor guppy

YouTube video

How Do Worms Get Into Fish Tanks?

Most of the time, tiny black worms get into your fish tank when:

  • you’re overfeeding your fish.

When you continue to overfeed your fish, you’ll be surprised at how much the tiny black worms can get in your fish tank. The left over food will rot in your tank and will produce the bacteria needed for these small black worms to form.

How Do I Get Rid Of The Little Worms In My Fish Tank?

One option would be to change the water in your tank. However, that would only be a temporary fix.

Other options you should consider include:

1. Keep your tank clean

If you want to get rid of the black worms in your fish tanks, you first need to know where they are. After you have identified that these black worms are present, you can go on to take critical actions against them.

One of them could involve taking down the tank and cleaning it the whole tank.

2. Don’t overfeed your fish

When dealing with a small tank, taking down the tank might sound like a reasonably great idea to rid them of black worms. But what happens when you are dealing with a much larger tank? What do you do in this case?

3. Treat the water

Use a worm aquarium treatment kit which you can buy on amazon.

4. Reduce the amount you feed your fish.

The trick is that these black worms flourish when there’s enough food to thrive on. When you stop feeding your tank, these black worms will die off on their own.

5. Use Copper

This is an extreme measure you can take against the black worms if they don’t go away. It is not the best option though- it’s just worth knowing. Adding copper to your fish tank might cause more issues- especially if you have some fish in your tank.

There are lots of fishes that are really sensitive to these additions. Also, copper is very bad for Shrimps, snails, crustaceans, and a lot of other life forms in general.

How To Remove Little Black Worms In Fish Tank Filter

If you have little black worms in your fish tank filter follow the below steps to remove them

  1. Remove the whole filter from your tank
  2. Remove the internal filter and rinse under a hot tap
  3. Rinse the rest of the filter under a hot tap
  4. Fill a bowl with hot water
  5. Place the whole filter in the bowl and leave for 1 hour
  6. Rinse under the tap again
  7. Perform a 50% water change in your tank
  8. Place the filter back in your tank

How To Identify Worms In Your Fish Tank

If your tank is newly set up, there are chances that you might be dealing with mosquito larvae and not real worms. How do you know? Really simple!

Most of those other black worms exist in overfeed tanks. Generally, in tanks that have been together for a long while.

In any case, to identify the worms in your fish tank, you might want to check on the body of the worms. Check if the tiny black worm has segments or not and classify as earlier discussed.

Are The Tiny Black Worms Dangerous To My Fish?

No. Most tiny black worms are generally harmless. A lot of hobbyists that have had experience with these worms believe that they are not dangerous to your fish and that they won’t hurt them at all.

The only threat black worms might pose to your fish is the possibility of eating your fish eggs. So, if you’re dealing with tiny black worms here, it might be wise to think about getting rid of them.

The decision to keep your worms or to let them go depends totally on you.

Are There Only Black Worms In Fish Tank?

No, not only tiny black worms are present in fish tanks. There are lots of other worms that find their way into it. White worms, grey worms, red worms also one way or the other get into the fish tank.

When these worms get into the fish tank, they exhibit similar behavioral properties to the black worm.

Why Are There Little Worms In My Fish Tank?

Planaria, tiny black worms, are the most common pest in aquariums. The triangular head of planaria, which can reach a maximum size of roughly 10 mm, makes them simple to recognize.

Planaria are small, black worms that, if there are too many of them in your aquarium, might harm your fish. Detritus worms can multiply quickly and become a problem due to inadequate cleaning schedules or overfeeding of fish.

Black Worms on Fish Tank Lid

Black worms that are constantly moving around in the fish tank are drain fly larvae. There may be drain fly larvae nearby your tank filter or tank lid. If you notice black worms, reduce feeding, change the water or use a treatment kit.

Drain fly larvae can only grow to a maximum size of 4 to 10 mm. Algae and the remaining food in the tank make up the majority of their diet.


These methods of getting rid of your worms would work. However, you might not be able to get rid of those worms entirely. As long as you keep overfeeding your fish, it is almost sure that the worms will keep coming back.

You must maintain a high level of hygiene for your fish tank. Clean it from time to time. The tiny black worms in your fish tank don’t have to be there.

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Hello, I'm Jason. I'm the guy behind HelpUsFish.com. I volunteer at my local fish shop and I created this site to offer tips and advice on the fish I care for.