3 Types of Tiny White Worms Found in a Freshwater Aquarium


Keeping aquatic pets can have its disturbing side.

For example, you’ve just discovered some tiny white worms crawling or floating in your freshwater aquarium.

However, you should not be alarmed before taking the time to identify the intruders.

Most of the time, these will be harmless species like the unsightly Detritus worm.

Nevertheless, that’s not always the case and sometimes you’ll need to get rid of the infestation quickly.

So let me help you in identifying and removing the small white worms that have overtaken your new aquarium.

What Types of Tiny White Worms Can Be Found in a Freshwater Aquarium?

There are two main types of small white worms that could populate a freshwater aquarium. One type is Nematodes, which are hair-like roundworms known as Detritus worms. The other type is flatworms and includes species such as Planaria and Rhabdocoela.

Identification of the species you’re dealing with is important, because while Detritus and Rhabdocoela worms are harmless to fish and shrimp, Planaria may not be.

I would strongly recommend using a magnifying glass when trying to identify your type of worm.

That being said, here’s where the population of worms in your aquarium came from:

A common way of introducing freshwater worms to a fish tank is through new aquatic plants, substrates, or decor. Overfeeding your fish or shrimp and not doing regular tank maintenance will provide enough leftover food for the worms to feed on. Eventually, the worm population explodes and this is when the fishkeeper sees a problem has occurred.

Detritus Worms

detritus worms on aquarium glass

by PandabearXp

Detritus worms are not one species of nematode but a collective term for all roundworms that may appear in a freshwater system.

These little freshwater worms are a natural part of the ecosystem and will usually inhabit the substrate of your aquarium.

There, they help with breaking down excess waste or uneaten fish food.

Usually, white Detritus worms will come out of the substrate when the oxygen levels in the tank are low.

When that occurs, you can find them crawling on the aquarium glass or floating through the water.

Anyway, it is highly unlikely that Detritus worms could pose a threat to your pet fish and shrimp.

These tiny nematodes are only interested in consuming waste and debris.

Detritus worms are more often seen in shrimp tanks because carnivorous fish would usually eat them.

You are not obligated to do anything when you see them, and most aquariums will have them.

Author’s note: The substrates of planted aquariums are even more likely to accommodate Detritus worms. That’s because in a planted tank the worms could have been introduced with the many live plants you’ve put in the tank.

It’s also easier for Detritus worms to find food in such systems because, often, aquarium plant fertilizers are being used.

Identification Guidelines

detritus worms in substrate

by mmandajade

Detritus worms can be identified by their very thin bodies which resemble a white thread or hair. They remain relatively small and, usually, will not be longer than 0.5 inches (1.27 cm).

Unlike flatworms, Detritus nematodes will seem very active and wiggly.

One sure sign that you’re seeing nematodes in your aquarium would be if the little worms float in the water.

Flatworms prefer to glide calmly and do not float.

How to get rid of the many Detritus Worms in your fish tank?

Though harmless to your fish tank and humans in general, Detritus worms can be unpleasant to look at.

If you’re dealing with an outbreak of white nematodes you should try to stay on top of the tank’s maintenance.

Regular cleaning will gradually reduce the worm population to normal levels.

That being said, here’s what you can try to get rid of unsightly Detritus worms in your aquarium:

  1. Reduce the amount you feed to your fish or shrimp.
  2. Vacuum the substrate more often.
  3. Oxygenate the water with an airstone.

Once the nutrients in the aquarium system are brought back to balance the Detritus worms will visually disappear.

It’s likely, however, that a small number of them will remain in the substrate.

Anyway, the frequent use of a gravel vacuum will aerate the substrate enough for Detritus worms to remain underneath it.

Also, attaching a simple air pump such as this one to an airstone helps with keeping the oxygen levels in your fish tank in the norm.

The higher oxygen content in the water will not force the Detritus worms to stick their heads out of the substrate.

Anyhow, a sudden swing in the water’s parameters could also bring these nematodes out. For example, it’s not unseen for them to start floating around after a large water change.

Author’s note: Guppies and Endler’s Livebearers absolutely love eating tiny roundworms. A small group of Guppies will eradicate a large population of Detritus worms in a matter of days.

Rhabdocoela Flatworms

rhabdocoela flatworms

by PuffedComma

The Rhabdocoela worms that you can see in your aquarium would be a type of freshwater flatworm that feeds on bacteria and microalgae.

These harmless flatworms will not prey on your fish or shrimp and are part of the natural ecosystem in the tank.

You may also find the Rhabdocoela worms swarming on plants or fish that are already dead.

Anyway, Rhabdocoela is one of the most common types of white flatworm seen in the aquarium hobby.

How to Identify Them?

rhabdocoela worm identification

by Clemsons2k

The Rhabdocoela flatworms are characterized by a very tiny size as they will rarely grow over 0.2 inches or 0.5 cm in length.

Another key component to their identification is that they will slowly glide on the aquarium’s glass and will not appear to wiggle like Detritus worms.

Rhabdocoela have two round ends and do not possess the typical triangle-like head of the larger Planaria.

Removing Rhabdocoela Worms

Same as with Detritus worms, Rhabdocoela populations are a result of too many nutrients in your aquarium system.

To get a Rhabdocoela population under control I recommend vacuuming the gravel of your tank more frequently.

Also, reducing the amount of food you offer to the system may help too.

Furthermore, most small fish with a predatory instinct will likely make short work of Rhabdocoela.

For example, Betta fish feed on small crustaceans and worms in the wild, and so will love eating Rhabdocoela flatworms.

Planaria Flatworms

planaria flatworms

by Ben Cantrell

Planaria are a species of carnivorous flatworm that is predatory in nature.

These worms are the ones you don’t want in your tank for too long.

Planaria can mainly be a threat to small freshwater snails and a shrimp population.

These worms would feed on shrimp eggs and baby shrimp at night.

Adult shrimp that are molting can also be at risk of a Planaria attack.

Anyway, some aquarists claim that they’ve witnessed Planaria worms paralyzing live adult shrimp.

This would imply that the flatworm uses a toxin of some sort.

I did some research on the subject and here’s what I found:

Freshwater Planaria are not known to have any toxins in their body but they are not a well-researched species.

I’ve also found a peer-reviewed study concluding that some land-based Planarian worms produce a neurotoxin called Tetrodotoxin.

However, the land-based Planarians seem more sophisticated than the ones we get in our aquariums.

Anyhow, Tetrodotoxin is the same neurotoxin that some marine pufferfish produce and there’s no antidote.

Another study I found during my research suggests that these pufferfish actually get the toxin from eating a type of marine flatworm.

This marine flatworm was not related to Planaria, however.

Anyway, there’s also this video that shows what seems to be a dying shrimp with a Planaria worm on it:

I think that it’s unclear whether or not the shrimp was already dying or is being killed, and the description of the video is quite speculative.

Key Traits to Identify

planaria identification

by Blakat014

Young Planaria look like small white flatworms that have a distinctive triangular head with two eyespots on it. Adult Planarians can grow up to 1.5 inches (3.8 cm), but will usually remain around 1 inch in body length (2.54 cm).

Adult Planaria worms can develop a pink tint to their body.

Another key trait of Planaria is that they move slowly and prefer to creep on surfaces.

They do not float or wiggle like round Detritus worms.

Author’s note: Often Rhabdocoela will get misidentified as Planaria. The difference between the two worm species is that Planaria grow considerably larger and have spade-like heads. Rhabdocoela, on the other hand, stay relatively small and have two rounded body ends.

More often than not aquarists would encounter Rhabdocoela in their tanks, rather than Planaria.
planaria vs rhabdocoela

How to Rid Your Tank of Planaria Flatworms?

Planaria flatworms are not usually an issue in tanks that house enough predatory fish.

As long as the worm fits in the mouth of a fish – it will get eaten.

The main issue arises when you have a shrimp tank where you can’t add predatory fish.

The fish will decimate the shrimp population even faster than Planaria.

Also, it can be very difficult to catch small fish.

So if you’re a shrimp keeper there are only 2 options left for you.

Take a look at the two methods that you can try to rid your aquarium of Planaria:

  • Kill it with a chemical treatment;
  • Naturally export the worms from the tank with a Worm Trap.

First, let me teach you the natural method as it’s always better to go that way when dealing with live animals.

1. Make a DIY Planaria Trap.

A worm trap, in the context of fishkeeping, is a container with holes that lures the worms in.

You put inside some food as bait and wait.

After that, you export the flatworms from your aquarium and repeat the process until all Planaria are gone.

There are different ready-made worm traps that you could get online and this is one such example that has a lot of positive feedback.
commercial planaria trap

by AC-Ninebreaker

However, I would recommend doing your own version of it for two main reasons.

Obviously, one reason is that you will save time and money.

The other, more important, one is that commercial worm traps are too small to rid your tank of a flatworm infestation quickly.

By making your own DIY worm trap you can export much more Planaria at once.

That being said, here’s how to make a Planaria trap yourself:

  1. Get a 16.9 oz plastic bottle of some sort.
  2. Rinse the bottle inside-out.
  3. Perforate 4 holes on the bottom of the bottle by using a needle or a pin.
  4. Put a very small amount of fish flakes inside the bottle.
  5. Put the cap on and tighten it.

After following these simple steps you’ll have yourself a DIY worm trap ready to be put in action!
diy worm trap instructions
Anyway, before I continue I need to explain some of the steps further.

Though the needle holes may seem too small, you should know that Planaria are very good at squeezing their bodies in tight spaces.

Make the holes any larger than that and you risk making the trap inefficient.

Another thing I would like to point out is that you should not put too much fish food inside the trap.

Otherwise you risk Ammonia and Nitrite levels rising which can be even more devastating to your shrimp colony than Planaria flatworms.

You could use any fish food that supposedly has meat in it, and you can use actual raw meat but in very small amounts.

The better the bait the more worms you’ll catch at once.

I prefer fish food because I don’t want to contaminate my shrimp tanks with something from the raw meat.

Anyhow, after your worm trap is done, you just put it inside your tank and wait.

Hold the bottle down while it fills with aquarium water and starts to sink.

Push the bottom of the bottle in the tank’s substrate with a gentle twisting motion.

Let it sit there in a straight position with the bottom slightly buried.

For the best results, set the worm trap right before lights out and take it out the next morning. Planaria are nocturnal predators and become most active during the night.

Anyway, the next day you may feel somewhat grossed out by the huge number of flatworms inside the bottle, but this means it’s working.

Get the bottle out and rinse it in your backyard or somewhere outdoors.

Author’s note: Never let Planaria go down the drain. You don’t want what happened in your aquarium to happen in your drinking water facility. I usually dispose of the worms over soil where they will dry out and get eaten by other critters.

Anyhow, repeat this process until there are no Planaria in the bottle the next morning.

A heavy worm infestation takes 3 to 4 days to get rid of.

2. Use a Dewormer.

A reliable way to kill Planaria is by using a dewormer of some sort.

Some aquarists swear by a canine dewormer known as Panacur C, which does work.

However, I prefer a more natural remedy known as No-Planaria. I’ve chosen the exact product in the link. Its active ingredient is an extract from Betel Nut, a type of palm tree.

Anyway, don’t forget to remove your carbon filter media before the treatment and follow the instructions on the label of No-Planaria closely.

The powder itself may cloud the water in your tank at first, but this will go away quickly.

Also, make sure to convert the gallon capacity of your tank in liters because that’s what No-Planaria use in their guidelines.

While doing the unit conversion try to estimate what volume of water the decor in the tank displaces and subtract that from the overall gallon capacity.

Anyhow, using No-Planaria does work and, as a remedy for flatworms, is safe for shrimp.

Unfortunately, some of your more sensitive freshwater snails may perish during the treatment.

However, what I would consider the biggest disadvantage of this Planaria removal method is the potential for ammonia spikes after the worms die out.

All of the Planaria worms will be dead in roughly 72 hours, but most of them can remain in your substrate.

There, they will start to decompose which can throw your tank’s parameters off the chart.

For this reason, I’d advise doing a thorough substrate vacuuming after the treatment is over.

By vacuuming the substrate you’ll rid your aquarium of the small leftover worms that have plagued it.

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