There are many types of worms in a fish tank; these worms may be parasitic, commensal, internal, or external. The parasitic aquatic worms act only in their best interests, often feeding off your fish and causing them harm.

The commensal worms contribute some form of resource to the host, like keeping the tank clean; other aquarium worms do not affect the fish and the tank environment.

You will learn how to tell parasitic and commensal worms apart, how to tackle them, and the best ways to prevent your tank from becoming overrun by these worms.

Let’s begin, shall we?

Types of Worms in Fish Tank

You can find many types of worms in an aquarium, from the basic flatworms to small white worms and the very prickly bristle worms.

1. Commensal Aquarium Worms

Commensal worms, unlike parasitic aquarium worms, do not harm your fish. Instead, they contribute to the health of your aquarium in unique ways.

Let’s explore Detritus, a famous commensal aquarium worm.

– Detritus Worms

Detritus worms are segmented worms that look like tiny white threads wriggling through the water. They are detritivores, so they feed on decaying plants and animal wastes only.

Thus, they pose no harm to your fish and, in controlled numbers, help clean your tank and maintain water quality in your tank. You can find detritus worms in most fish tanks because of the variety of ways they can be introduced.

Some means of Detritus worm introduction: new fish, plants, substrate from another tank, etc. They tend to favor gravel; thus, it is not uncommon to find them in between the pebbles.

You may not see the Detritus with your eyes until time for proper clean-up with the vacuum. If, however, you can see them coming out of the gravel in the tank frequently, it means they have accumulated, and it necessitates prompt action.

a) How Do I Know There Is an Explosion of Detritus Worms in My Fish Tank?

When you begin to actively see these white thread-like annelids wriggling up and down in your tank, you know immediately that their population has drastically increased. You might see a couple of these white worms in aquarium, clinging to the sides of the tank or floating at the water surface in a ring-like formation.

Another way to know that you have a Detritus worm problem is the appearance of colonies from the tank filter. Usually, in this case, when you start up the filter after a scheduled water change, you’ll see these worms drift out.

b) What Causes Accumulation of Detritus Worms?

Poor tank maintenance is the chief cause of an abundance of Detritus in the tank. Lack of thorough tank cleaning; or periodic maintenance favors rapid Detritus reproduction. With poor water conditions, there is a decrease in both pH and dissolved oxygen; consequently, you see the worms wriggling to the surface of the tank to seek out more oxygen.

c) How to Remove Detritus Worm

Start first by changing the water in your tank to remove many of the Detritus worms and their food sources.

Next, clean your tank thoroughly; you’ll need a gravel vacuum for this. The worms will be clustered at the sides and bottom of the fish tank.

Inspect your filtration system to ensure it is working as it should; if not, replace it. Your water needs to have the proper pH and dissolved oxygen concentration to prevent the influx of Detritus worms in your aquarium.

Once you are done with steps 1-3, refill your fish tank slowly, checking that the water parameters are within the acceptable limit.

d) How to Prevent Accumulation of Detritus Worms in Your Aquarium

With these tips listed below, you can prevent your fish tank from being overrun by the Detritus worms.

  • Clean your tank substrate regularly; if you have plants, gently place your gravel vacuum on them.
  • Review your feeding practice to find new ways to optimize the process; one way is to stop overfeeding your fish.
  • Ensure your fish tank is not overpopulated with fish and that the fish are getting enough food without generating so much waste.
  • Ensure that you do a 25-50 percent water change weekly to rid your fish tank of the built-up wastes.

These simple steps, if done regularly, will help regulate the Detritus population in your fish tank and improve your tank’s health over time.

2. Parasitic Aquarium Worms

Parasitic aquarium worms contribute nothing to your fish health and tank environment.

Instead, they affect your fish negatively, competing for nutrients with your beloved fish and even feeding on the fish. Their parasitic behavior creates a great deal of stress for the fish and leads to increased disease spread and fish mortality.

We have outlined some of these common parasites in fish tank.

– Trematodes – Flukes

Flukes are microscopic worms that you cannot see with your naked eyes; however, they are guaranteed to pose a problem at least once in every aquarists career. In small numbers, they do not cause much harm; however, when there is a spurt in their numbers, you will start to see more and more of your fish falling ill.

Clinical signs of Fluke induced sickness include reddish irritated fish skin, flashing behavior, and strange swimming patterns.

– Crustaceans – Anchor Worms

Anchor worms are another typical example of aquarium worms that can make life unbearable for any fish keeper. Only the reproductive parts of anchor worms are visible to the naked eye. They burrow deep into the muscles of your fish and cause ulcers.

Signs that your fish is infected with anchor worms include strange swimming patterns, reddish irritated skin, and in bad cases, fish ulcers. The good thing about this particular worm is that it can be diagnosed and treated quickly.

We recommend that you change your tank water to remove most of the worms and then follow up with the recommended treatment to kill off both the adult and baby worms.

– Planarium

Planaria are tiny aquarium parasites constantly on the move, looking for meaty food to feed on. They will eat uneaten fish food in the tank, shrimp eggs, fry, fish, etc. Thanks to their parasitic feeding, they can decimate all your breeding efforts and pose a severe threat to your tank.

For the most part, they do not eat adult fish and shrimp; but before you start to rejoice, this is because these fishes move too quickly for them. However, they have no issues crawling all over fish and shrimp at rest and taking bites out of them. So yes, Planaria is not something you want in large numbers in your fish tank.

Planaria are flatworms that thrive in saltwater and freshwater and are related to the flukes and nematodes. While planaria will not harm your healthy fish, they love to eat fish eggs and eat the eyes and gills of sick fish. This makes them highly problematic to aquarists.

– Annelids – Fireworms, Bristle Worms, and Leeches

The worms in freshwater aquarium that most fish keepers are conversant with are annelids. In this class, bristle worms are familiar residents of saltwater tanks. These bristle worms have a powerful defense system; they sting.

Their close cousins, the Fireworms, pose an even more significant threat to invertebrates. Bristle worms and Fireworms feed on leftovers from your fish’s meal; thus, one way to prevent an infestation is to provide your fish only what they can finish at a go.

Amongst the annelids, leeches are another problematic group. They fasten themselves to the sides of the fish or even to the fish’s mouth and secrete substances that adversely affect the fish. The adult leeches are easy to spot and pick out. However, you’ll still need to tackle their eggs if you are to rid your tank of the plague that they present.

– Nematodes – Roundworms and Hookworms

Roundworms and hookworms are typical examples of nematodes in fish tank. Their lifecycle affects many aquatic invertebrates; thus, you must understand how each lifecycle affects your fish. For example, the larva stage of hookworm causes Larval migrans, a disease that affects the tissues of the fish.

How to Treat Your Aquarium for Parasitic Worms

Now that you know some of the common parasites in fish tank, let us progress to how you can rid your tank of these suckers.

The first step is to identify the exact type of parasitic worm in your tank. You can seek help from a trained vet to help with the correct diagnosis.

Once you have correctly identified the parasite type, you can treat the infestation with the prescribed medication.

NOTE: It is vital to use an antibacterial drug specific for that parasite problem to avoid breeding antibiotic-resistant species.

3. Tiny Aquarium Bugs

Most aquarists have had issues with tiny white bugs in aquarium at some point or the other in their careers. These bugs are tiny shrimp-like crustaceans that most likely belong to the class of copepods or amphipods. They are free-swimming and benthic. Copepods can be found in any aquatic habitat; salty, brackish, or freshwater, while amphipods are found majorly in saltwater habitats.

Together, copepods and amphipods are referred to as zooplanktons and serve as food for the fry in the tanks. A few adult fish, like the Mandarin fish, rely on copepods and amphipods for their food. Even though these zooplanktons make great snack options for your fish, keeping their population under control is essential.

– Why Are My Fish Restless?

One reason why your fish is restless is bugs. These tiny creatures crawl on your fish, causing an annoyingly tingling sensation that makes it difficult for them to rest. The fish often dart around, shuddering, in an attempt to get these tiny bugs off.

– How to Get Rid of Tiny Aquarium Bugs

As with all things, moderation is critical; thus, you must control the bug population in your tank. A sure way to rid your tank of these pesky bugs is to add a hang-on-tank type of filter, preferably one with a pleated cartridge and delicate micron sleeve.

Why Are There Worms in My Aquarium?

Most aquarists ask why there are tiny white bugs in their aquarium. One answer is that the tank has poor water quality, i.e., the tank is not thoroughly cleaned, and some water parameters are off. Worms thrive in unclean environments, so if your tank water is not changed as often as it should, you can expect a worm infestation.

Another reason why worms are thriving in your aquarium is overfeeding. When you throw in more food than the fish can it, it settles at the bottom and becomes food for the worms to feast in. And, of course, where there is a surplus of food and favorable tank conditions, the worms will multiply rapidly.

How Can I Eradicate Aquarium Worms?

If you discover tiny white worms in your aquarium, it is one of two things. The white worm can either be a Detritus worm that can be taken care of with proper aquarium hygiene or Planaria worms that are more challenging to handle.

Before deciding on a course of action, you must know which class of white worm you are battling. Only when you have identified it can you understand if thorough cleaning will solve your worm problem, or you’ll need a more decisive course of action.


  • Without proper tank hygiene, your fish tank may become overrun with tiny aquarium worms
  • Some of these worms are parasitic, causing harm to your fish and its environment; others are commensals
  • Some of these worms make excellent snack options for your fish

There are various worms in fish tank; the ones that harm your fish and those that don’t bother it. One easy way to ensure your tank is free of parasitic worms is to maintain proper tank hygiene and proper feeding. We hope this article has equipped you with all you need to know about worms in your fish tank. We’d love to answer any questions you have.

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