Why Are There Black Worms In Your Aquarium (& What To Do)

Last Updated on 2023-08-30

Any fish tank owner who cares about their aquarium’s aesthetics may find the presence of black worms to be the most concerning problem they face. You should know if they are bad for your fish beyond just your personal dislike for them. Many types of aquarium-dwelling worms, all of which are black, share the common name “black worms,” including drain fly larvae, blood worms, and planaria.

Fish tanks may host either free-living black worms or parasitic worms that feed off the fish. The best way to get rid of black worms is to familiarize ourselves with them. Keep on reading!

What Are Blackworms?

A wide variety of worms that live in aquariums are collectively referred to as “blackworms” due to their common slang name. The majority of the time, these worms have a black appearance, but the physical characteristics of every single worm are unique.

There are species of black worms that are helpful to fish, while other species might be detrimental to fish. They can be free-swimming or parasitic, with some species inhabiting the fish themselves and others swimming freely in the tank. Those that are allowed to freely move about the aquarium won’t harm your fish and can provide an excellent source of nutrition for them, but they can detract from the aesthetic value of the tank. 

When dealing with parasitic black worms, it is imperative to exercise caution and take immediate action.

What Are The Little Black Worms In My Fish Tank?

Aquarium enthusiasts often come across small black worms in their tanks and wonder what they are. These creatures are commonly known as black worms, but they can actually refer to a few different types of aquatic animals. Black worms can be drain fly larvae, blood worms, or planaria, among others. While they share the common trait of being black, these creatures can vary greatly in appearance. Drain fly larvae, for example, are thin and translucent, while blood worms are red and segmented. Planaria are flat and slender, with a head that is distinct from the rest of their body. 

Blackworms can also be a nuisance if they reproduce too rapidly. They can quickly overrun a fish tank and cause problems for the fish. If you have too many blackworms in your tank, you may need to remove some of them.

How To Identify Worms In Your Fish Tank

Worms are pests that can infest freshwater aquariums. These pests can cause a variety of problems for your fish, including stressing them out, lowering the water quality, and potentially causing disease. While there are many different types of worms that can infest your tank, there are a few key ways to identify them.

  • First, you should focus your attention on how they move. Do they move like earthworms crawling along the glass, wiggle, or just glide along the surface? This will assist you in determining the specific species of worm that you are dealing with.
  • Second, you should evaluate the shape of their body. Have they been described as having a round or flat body, or do they have a definite head shape? Once more, this will assist you in determining the species of worm.
  • Finally, make a mental note of the parts of the tank in which you are finding them. Where exactly are they located; on the glass, in the water column, or in the substrate itself? This will assist you in determining the severity of the infestation as well as the type of treatment that will be required.

If you’re unsure what kind of worms you’re dealing with, it’s always best to consult with a qualified aquarium specialist who can help you identify them and recommend the best course of treatment.

How To Get Rid Of Black Worms In Fish Tank

The elimination of black worm parasites from a fish tank is a difficult job. In extreme cases, a copper treatment may be necessary to control the spread of black worms. Nonetheless, copper treatment poses a threat to all the invertebrates in your tank, including shrimp, snails, crustaceans, and even certain fish.

So, the easiest way to get rid of black worms in fish tanks is to use natural ways. Here are a few suggestions for getting rid of the black worms in your tank:

Replace Half the Water in Your Aquarium Regularly

Maintaining a clean aquarium is the first line of defense against black worm infestation. This is why it’s a good idea to regularly replace at least half of your tank’s water. If there are any obvious black worms in the tank, you should get out the vacuum and get rid of them.

Apply Bleach to the Decorations, and Everything Else

You can prevent the black worms from multiplying by keeping your tank clean. To clean your tank, take everything out and soak it in a bleach solution for five minutes. Then, after three or four hours, you can clean them with water and return them to the fish tank.

Take Care Not to Overfeed Your Fish

When there is plenty of fish food in the tank, black worm populations rise. Stopping the excessive feeding of your fish will result in the death of the black worms because they will no longer have enough food to survive.

Dose Your Tank with Worm Medicines

There are a number of medications that can eradicate the black worms in your aquarium. They are widely available at local pet stores and on the internet. The kind of medication you’ll need to treat the black worms in your tank will vary depending on the species of worms you have. It’s important to read the directions on the medication bottle before adding it to the tank. It’s important to be aware that some medications can be hazardous to aquatic life in an aquarium.

Check to See if Your Fish and Plants Are Healthy Before You Buy Them

Black worms can be a problem if they get access to the aquarium by latching on to the fish or plants. To prevent the introduction of black worms into the fish tank, it is vital to inspect the fish and plants prior to purchase. You may prevent the introduction of black worms into your aquarium by maintaining a 30-day quarantine period for all new fish and plants.

Cleanse Live Aquarium Plants With Potassium Permanganate

Potassium permanganate is the treatment of choice if black worms have invaded your live aquarium plants. You should soak the plants in the potassium permanganate solution for five minutes. If you really want to get rid of those black worms, you’ll need to do this procedure every two days.

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Why Are There Black Worms In Your Fish Tank?

Black worms are a widespread commensal that hitch rides into aquariums on live plants and other organic matter. Blackworms are a common pest, but there are several varieties, and some of them will be beneficial to your fish while others may do them harm. They occur normally in aquatic environments.

Black worms can invade your aquarium through the substrate, filter media, socks, or any other porous material.

There are three primary causes of black worms in a fish tank:

Poor Water Quality

It indicates that the tank has not been properly cleaned and that the water’s parameters are likely wrong. It’s likely that you’ll have a black worm problem if you don’t regularly replace your tank water, as black worms prefer dirty environments.


Throwing in more food than the fish can consume causes it to sink to the bottom, where it is then consumed by the black worms. And naturally, black worms will proliferate swiftly in a tank with an abundance of food.

The New Additions

Carrying in some new substrate from another tank is a good way to introduce black worms to yours. Black worms can also hitchhike into your aquarium on live plants and fish. Before you put anything into your fish tank, make sure you’ve properly disinfected it and put it in a quarantine period.

It’s not always necessary to get rid of black worms in your aquarium, but their presence usually means you need to check on anything else. Before deciding on a plan of action, it’s important to take an honest inventory of your tank’s current condition.

How To Prevent Black Worms In Your Fish Tank

Once an outbreak has been contained, preventative measures should be implemented. Reducing the amount of dirt that builds up in the aquarium is the most effective method of keeping black worms at bay. This usually involves breaking out of routines.

Here are some measures you can take to keep the black worms from destroying your fish tank.

Clean your Substrate 

Maintain a regular cleaning schedule for the substrate in your aquarium; if you have plants, you can gently place the gravel vacuum on them.

Avoid Overfeeding

Stop overfeeding your fish as a starting point in optimizing your feeding routine.

Avoid Overcrowding

Make sure your fish tank isn’t too crowded and that they’re getting enough to eat without wasting too much food.

Water Change

Be sure to do a weekly water change of 25-50 percent to remove waste buildup in your fish tank.

Quarantine All New Additions

Properly quarantining new additions to the fish tank is the single most important thing a fish keeper can do. Whether they are fish, invertebrates, or plants, quarantining them helps prevent the spread of black worms. It’s best to observe any disease processes for four to six weeks in a completely separate system.

If you follow these steps on a regular basis, you can keep the Detritus population in your fish tank under control, which will ultimately benefit the tank’s health.

Black Worms In Fish Tank 

There are numerous species of black worms that can invade your fish tank. These are some of the most frequent species of black worms seen in a fish tank:

Drain Fly Larvae

Drain fly larvae are active black worms that move around in the fish tank. Drain fly larvae can seem like black worms and can often be found near the filter in your aquarium. Larvae of sewer flies rarely grow larger than 4-10 mm in length. Algae and scraps from the tank’s food supply make up the bulk of their diet.

 Blood Worms

If you look at a blood worm with a black light, you will see a red color. Many different kinds of worms feed on blood, including mid-fly larvae and the worms of the genus Glycera. These worm-like creatures won’t hurt your fish in any way. They can swim around freely in fish tanks and are food for fish.


Little black worms called planaria are the most prevalent aquarium pest. Planaria can grow to a maximum size of about 10 mm and are easily identified by their distinctive triangular head. Planaria are tiny black worms that might cause difficulties for your fish if there are too many of them in your aquarium. However, if there are only a few of them, you probably don’t need to worry. While they pose no threat to healthy fish populations, these worms can quickly destroy populations of weaker species.


Leeches are a species of little black worm that aren’t naturally found in an aquarium. Rather, they are typically transported from live aquarium plants. These black worms are food for the fish that eat other fish in the tank. Before putting any plants into your aquarium, be sure none of them have leeches. It’s really challenging to remove leeches from a tank after accidentally adding plants that contain them.

Mosquito Larvae

Even with fresh, filtered water in a brand-new fish tank, mosquito larvae can develop. Nothing to worry about here; these black worms, about a quarter of an inch in length, will mature out of the tank and disappear.

Lumbriculus Variegatus

This black worm prefers a watery environment, where it can reach a maximum size of four inches. Lumbriculus variegatus, with its tube-like form, is a nutritious fish meal.

What Are The Black Worms In Fish Tank Gravel?

Detritus worms and planaria are the two species of black worms that are most frequently seen in gravel. In the same way that earthworms move about, black worms can be found moving around in the gravel or plant substrate. It’s possible that the only moving things you notice in your substrate are one or two. Alternately, you might have noticed large groups of them wriggling around.

Sometimes you’ll notice them sticking half of their bodies out of the gravel in a large bunch, like a shag carpet made of worms. Other times, you won’t see them doing this. This behavior will appear as a result of the worms’ overpopulation, which has caused the oxygen levels in the tank to drop due to the large number of worms present. They are attempting to breathe, which causes them to protrude parts of their bodies above the substrate in order to increase the amount of oxygen that is available to them.

How Long Do Black Worms Survive In A Fish Tank?

If you want to give your fish the very best diet possible, live blackworms are an excellent choice. Not only are they abundant in protein and nutrients, but they are also capable of surviving in a freshwater tank for an infinite amount of time. This means that, in contrast to other foods, they will never cause the water to become contaminated. They will continue to exist until they are consumed by your fish.

Where Do Small Black Worms In Your Fish Tank Come From?

Overfeeding the fish in your tank and introducing live aquarium plants both increase the risk of black worm infestation in your tank.  When you overfeed your fish, you make it possible for some black worms to survive in the aquarium by providing them with enough food. They end up reproducing, which leads to an increase in their population within the tank.

The spoiled food will be left in your tank if you don’t remove it. Because of this, bacteria will be formed, which is necessary for the presence of black worms in the tank.

Also, there is a possibility that some worms will become attracted to the live aquarium plants or any other ornamental things that are placed in the tank.

Should You Put Black Worms In Your Fish Tank?

Yes, live blackworms are among the greatest foods that you may provide for your fish to eat in your fish tank. Not only are they abundant in protein and nutrition, but they have the ability to live for an infinite amount of time in a freshwater tank. This means that, in contrast to other foods, they won’t ever pollute the water and will continue to exist until they are consumed by your fish.

One of the primary advantages of putting blackworms is the fact that they are one of the live foods that are cultured with the least amount of effort. They are also tougher than many other live foods and don’t die off as often as daphnia or adult brine shrimp.


How to Culture Blackworms?

A photoperiod of 14-16 hours of light and 8-10 hours of dark is ideal to culture blackworms. Blackworms require flake or sinking fish food to be fed to them on a daily or weekly basis for maintenance. Prior to feeding the blackworms again, make sure they have finished the food you gave them the last time.

Are The Tiny Black Worms Dangerous To My Fish?

Your mature fish do not need to be concerned about the vast majority of tiny black worms. These black worms have only one possible food source, which is the eggs of your fish. As a consequence of this, the fish in your tank will have a more difficult time reproducing.


A fish tank full of black worms might actually be home to several distinct species of worms, all of which look the same at a casual glance but are wildly diverse under the microscope. Depending on their nature, these black worms can either hurt or help the aquatic life in the fish tank. Black worms make a good meal for fish.

It’s not impossible to rid a fish tank of black worms, but it is difficult. The only kind of black worm that will hurt your fish is a parasitic one. Just remember, anything that doesn’t seem right in your tank should be looked into.

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