Planaria Flatworms in Fish Tanks – Everything You Should Know

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Planaria flatworms – an aquarist’s worst nightmare. These tiny worms are very dangerous to shrimp. If they infest your aquarium, they’ll slowly kill off everything in it. These worms are also very small, so noticing them isn’t the easiest thing in the world. But you’ll eventually notice the white blurs swimming about.

Planaria flatworms can reproduce asexually so all you need is a single flatworm to infest your entire aquarium. Most likely, you brought them from your local store, which got them from a supplier. Planaria worms will hitchhike on almost anything, including plants, crevices, and even fish.

Below, you’ll find a guide on planaria flatworms, how to get rid of them, and what danger they pose for marine life!

What is Planaria?

Planaria is a name given to one of the most common aquarium pests. Planaria are a species of free-living flatworm that hides under rocks and debris in marine habitats. These worms feed on fish waste, but they also prey on small aquatic life such as small worms, shrimp, shrimp eggs, snail eggs, and even live fish food like bloodworms or daphnia.

As their description suggests, these worms are, first of all, flat. But their distinguishing characteristic is their triangle-shaped head. These worms are very small and easy to miss if you aren’t actively looking for them. They can be as small as 0.1 in long. At most, they can grow to an unimpressive 0.6 in. But if you can get a good look at them, their triangle-shaped head is unmistakable.

These worms can be either white or different shades of brown, but you might also see some pink planaria. Their body color depends on their species, but also their diet. It doesn’t matter much though, because they’re all equally annoying. They’re aggressive, they eat anything they can, and they can even attack larger aquatic creatures and feast on them while they’re still alive.

And if you hoped that they’re easy to get rid of, think again! Planaria reproduce asexually. Even if you get rid of most of them, all it takes is one little worm to start reproducing in large numbers.

And did I mention that these ugly shovel-headed worms leave a trail of toxic slime behind them? And that this toxic slime is deadly to certain aquatic species? Clearly, not one nice thing can be said about this demonic spawn of a creature.

How to Get Rid of Planaria Worms?

Sadly, these slimy flathead worms are quite difficult to get rid of without some extra assistance. You can’t just scoop them out because they’re incredibly small and easy to miss. And if you forget just one worm behind, all your work will go to waste, because these suckers multiply all by themselves.

But not all hope is lost! Quite the contrary! There are some very effective and low-effort solutions to get rid of these annoying worms. All you have to do is set up the tank using any of these options, and watch as your planaria infestation will take care of itself! So, let’s take a closer look at these easy solutions.

– Planaria Trap

The first and simplest option is installing a planaria trap. I’m a big fan of this one from Aquarium Supplies. It’s affordable, reusable, and almost elegant in its simplicity.

Basically, this trap is just a 5” by 0.86” glass tube. There are three small holes alongside this tube, so it can trap multiple flatworms simultaneously. The design is very easy to navigate on the way in.

But once inside, the worms won’t be able to make their way back out. As a bonus, this little gadget can also help catch other types of worms as well as leeches. So, you can use it for multiple types of infestations.

To set this trap, all you have to do is place some bait inside the tube. Anything meaty will work, but dead shrimp, dead small fish, or raw pork liver are the best. Fill the tube with water, put the lid on, and then place the trap on the aquarium bedding with the holes facing downwards.

I should mention that this trap is sadly not safe for shrimplets. Small-sized shrimp can also get trapped inside. However, this works fine for aquariums with larger shrimp, snails, or even fish.

– NoPlanaria

If manually setting up a trap isn’t for you, don’t worry. There are also brilliant options for those who want to unleash chemical warfare. NoPlanaria is a quick, highly effective, virtually foolproof flatworm killer.

This product is all-natural and completely safe for plants, fish, and shrimp, but very aggressive against planaria. It contains Betal Nut Palm Extract, which is toxic to flatworms, nematodes, but also most snails. If you want to keep snails, you should rehome them while applying this treatment.

This stuff is so easy to use, it won’t take any more than 2 minutes of upfront prepping. For a very aggressive attack against flatworms, the recommended dose is 1 spoonful per 50 liters for 24 hours.

You’ll have to keep dosing down for 72 hours according to package instructions. By this point, you should’ve successfully eliminated the planaria in your aquarium.

Just remember to remove the carbon from your filter throughout the NoPlanaria treatment. After 72 hours, just perform a small water change (about 25%) and put the carbon back in your filter.

– Dewormer

Most dewormers are going to work well on tank intruders like planaria. Typically, fenbendazole-based dewormers are most readily accessible. They’re also among the most potent dewormers out there.

They work on both planaria and hydra, but they’re also very dangerous for shrimp and snails. You need to be very careful when using fenbendazole dewormers.

Dosing is difficult to get right, especially if it’s the first time you’re dealing with a planaria infestation. And most online tutorials offer contradictory advice.

You might see recommendations going anywhere between 0.1 to 1ml per 10 gallons. Lower doses are less likely to affect your shrimp population, but there’s no guarantee that all your shrimp will be fine regardless of the dose.

Timewise, Fenbendazole is as effective as other popular planaria killers. It should take no more than three days for all the planaria to die. However, if the planaria infestation is really bad, you might need to dose again after three days. You should perform a water change after each dose has run its course.

– Planaria Eating Fish

Another way to get rid of these worms is by adding planaria-eating fish to your aquarium. And there are many fish that love eating planaria, so you’ve got plenty of colorful options.

Freshwater Angelfish, Betta fish, and Tiger Barbs are particularly ferocious when it comes to live food. These species will prey on and eat planaria with abandon. These worms make a tasty and nutritious treat, as they’re rich in protein and fatty acids.

Other fish species that can help you keep the planaria numbers in check include Guppies, Mollies, Fancy Goldfish, Sparkling Gouramis, and Pearl Gouramis. These fish are omnivorous but don’t have a huge appetite. Still, they will snack on flatworms and flatworm eggs if given the chance.

But you don’t have to rely on fish alone to get rid of a flatworm infestation. You can also combine various extermination methods for the best results.

How do Planaria Reproduce?

As I’ve already mentioned, Planaria reproduce asexually. But this is just the most common way they do it. Planaria worms can also reproduce sexually, and this reproduction mechanism helps with increasing biodiversity within the species. Planaria worms are hermaphroditic, so they have both male and female sexual organs.

This means that any two worms can reproduce without any issue. Sexual reproduction in this species takes place through eggs. Planaria eggs can withstand even the most unfavorable water conditions, so they’re not likely to be affected by wild swings in water temperature, pH, or hardness.

But asexual reproduction is by far the quickest and easiest means of multiplying for these worms. And this style of reproduction can happen in two ways. The first is through tail-dropping. When water conditions are unfavorable, Planaria will spontaneously drop their tails and multiply. The head and the tail parts will regenerate and grow into full worms.

The second way this happens is through fragmentation, which can be either voluntary or accidental. During fragmentation, a planarian starts tearing its own body in half through a process known as “binary fission”. Once fully separated, the tail part grows a new head, and the head grows back its tail. In the end, you get two genetically identical worms.

If a planarian is crushed or ripped apart by accident, it can also regenerate in the same way. You could say these worms are immortal because it doesn’t matter how you slice them— they’ll always grow back.

Whether cut lengthwise or otherwise, a flatworm can regrow its body in a matter of one week. It’s actually puzzling, but you can cut a planarian into a piece as small as 1/279th of its original size, and it can still regrow to full body size.

Are Planaria Harmful to Fish?

Planaria don’t pose much of a threat to fish. At least not directly. In fact, many fish species like snacking on these little worms. These guys make a tasty, protein-rich treat for a variety of carnivorous, but also omnivorous fish species. Still, there are some instances where planaria can cause harm to your fish.

Planaria multiply very quickly and they will feast on anything small enough to eat. Adult fish aren’t in danger, but newborn fish and fish eggs are still vulnerable. In this sense, planaria can still make a dent in the fish population. If you keep egg-laying fish, you might want to rehome the mothers to protect the eggs and fry.

Are Planaria Harmful to Shrimp?

To put it bluntly, if shrimp were to have an arch-enemy, it would most likely be a planarian flatworm. Nothing will curb a planarian’s appetite for tasty baby shrimp. Planaria also eat shrimp eggs like there’s no tomorrow. If your planaria infestation goes on for too long, these little pests will definitely decimate your shrimp population.

If hunger strikes really bad, larger planaria worms will even attack and kill adult shrimp. Brown and black planaria worms aren’t as hostile towards shrimp as white worms are. However, they’re still wholly capable of hurting and killing them.

Are Planaria Harmful to Snails?

Planaria don’t just threaten shrimp. They’re also dangerous to gastropods. Remember that planaria are carnivorous and that they’ll eat anything small enough. They also attack larger creatures, especially if these have weaker defenses. And snails are sadly a good candidate.

Snail eggs and young snails are particularly vulnerable. But planaria will attack adult snails as well, slowly eating them alive. Also, unlike shrimp, snails are sensitive to most anti-planaria treatments, so it’s a lot harder to get rid of these pests in a snail tank.

Are Planaria Harmful to Plants?

As nasty as they are, at least planaria are harmless to plants. These flatworms are carnivorous, after all. They have no interest in eating plant matter, and will thus leave your plants undisturbed. And luckily, most planaria treatments are harmless for plants.

However, these worms climb and hide in the foliage. While they do so, they leave a trail of toxic sludge behind them. This mucous substance won’t affect plants but can be deadly for shrimp. As a result, you might still have to get rid of or clip your plants after removing all planaria from your tank.

Are Planaria Harmful to Humans?

Certain flatworm species can cause dangerous long-term infections in humans. Luckily, planaria isn’t one of them. You’re in no danger, as planaria are harmless to humans and most large organisms. In fact, planaria is among the very few free-living flatworm species.

This means that they aren’t parasitic in the true sense of the word. They are a pest, but they can’t infect and inhabit a living organism. Still, it’s best to exercise caution when handling or disposing of these worms, as you could accidentally contaminate new surfaces outside the aquarium.

Is Planaria Bad for Aquariums?

As we’ve discussed so far, planaria can mean big trouble if you’re keeping shrimp or snails. Otherwise, planaria aren’t dangerous to aquarium inhabitants. At least not directly. However, it’s not a good idea to let these creatures slug around.

White planaria are still a danger for small fish. These worms are aggressive and have a ferocious appetite. Black and brown planaria can also pose a threat, especially to fish eggs. If you’re trying to breed or maintain a stable fish population, these guys aren’t your friends.

Not to mention that planaria will even eat animal-based fish feed, keeping smaller fish from eating their fair share. Overall, even if they aren’t a direct issue, there’s really no benefit to keeping them around.

Will Bleach Kill Planaria?

Bleach is a highly potent disinfectant. If you want to get rid of flatworms and worm eggs, it’s definitely going to get the job done. However, you might also end up hurting the shrimp, snails, and fish in the aquarium. If you don’t rinse the aquarium properly before reintroducing your fish, you will inevitably hurt them in the process.

A lot of people recommend a bleach dip to disinfect aquarium plants. It’s true that bleach will outright kill all planaria and planaria eggs. But most aquarium plants are too delicate to withstand such strong chemical treatments.

Java Ferns, different Anubias species, and Buces are rather hardy, so you might try a 2 to 3-minute bleach dip on these plants. It’s best to use a small sample before soaking all your plants though. Just use a 1:25 mixture of regular bleach to tap water. After a 2-minute soak, discard the water and rinse the leaves thoroughly.

Will Aquarium Salt Kill Planaria?

Technically, salt can kill planaria but only if you apply it directly to the worms. Adding salt into the aquarium is likely to be useless and it won’t kill the little buggers. Salt isn’t toxic enough for them. Unless you pour incredible amounts of salt into your aquarium, the planaria won’t die from a few pinches.

I recommend sticking to the basics and using NoPlanaria or a planaria trap. They’re very efficient, and NoPlanaria is very safe for shrimps. It’ll only target the worms and isn’t toxic to anything else. Talk about no tradeoffs!


There you go. Now you know what planaria flatworms are, how they reproduce, where they come from, and how you can remove them from your aquarium. Planaria traps, Dewormer, and NoPlanaria are the best solutions to this infestation problem. Use them as soon as you notice any signs of worm activity in your tank!

Author Image Fabian
I’m Fabian, aquarium fish breeder and founder of this website. I’ve been keeping fish, since I was a kid. On this blog, I share a lot of information about the aquarium hobby and various fish species that I like. Please leave a comment if you have any question.
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