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Planaria in the aquarium: Eliminating flatworms

Last Updated November 17, 2020
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If you’ve been an aquarist for a while, chances are you’ve spotted these white worm-like creatures crawling on the glass. Ew! Luckily, they’re not harmful to most aquarium inhabitants.

Keep reading for more information about planaria, how to identify these creepy worms and what to do about them.

What are planaria?

Planaria (singular: planarian) are flatworms that appear in many shapes and forms throughout the world in both fresh- and salt water. Unfortunately, they can also sometimes be found in our own aquariums since they’re expert hitchhikers! They can hide away in plants, substrate, rock crevices, and even attach themselves to fish for a free ride. They’re rather common, so most fishkeepers will deal with these pesky aquarium worms at some point during their fishkeeping career.

Since there are so many types of aquarium worms, how do you know if you’re dealing with planaria specifically? If the aquarium worms in your tank are about 10 millimeters long, flat, have a distinctly triangular head, and glide across the glass with ease, you’re probably dealing with a planaria infestation. They are also typically whitish in appearance, although can be found in shades of brown as well. They may even be pink depending on what kind of food they’re feeding off!


Note: if you find white worms in your aquarium that are tiny, stringy and wriggly and mostly stay near the substrate, they are likely not planaria. They are detritus worms that, like planaria, appear when there is too much excess food.


Are planaria dangerous?

Planaria can be found in almost every aquarium, which is usually no problem since they are generally harmless. In fact, you may see one or two lone white worms in the aquarium and dismiss them. It’s only when you suddenly see hundreds of unsightly white worms bravely cruising along the glass that you’ll suddenly realize that you have a problem.

If you see these white worms, it’s a sure sign that you’re overfeeding your fish or shrimp. Luckily, if you only keep fish, planaria typically won’t pose a real threat. In fact, some fish species, like Bettas and pleco varieties, are actually said to view them as a tasty snack!

While planaria may not harm fish, if you’re a shrimp keeper, planaria may prove to be more of a headache. Some of these flatworm species are predators that prey on anything small that comes their way, including eggs, shrimplets, other worms, and sometimes even adult shrimp.

Eliminating planaria

Removing planaria from your aquarium can be quite difficult since they thrive off of leftover food. What makes the situation worse is that these white worms are asexual, so stopping them from reproducing while they have a buffet is nearly impossible. However, there are a few things you can do to battle a planaria infestation:

  • If you want to get rid of planaria for good, the most important thing is to cut back on feeding. If your fish/inverts fail to eat all the food, remove it in a timely manner, such as by using a siphon. This should prevent a new planaria infestation and help you battle the current one. It’s also better for the overall health of your aquarium since excess food can result in ammonia spikes as well.
  • If you don’t want to use medication getting rid of all planaria is difficult. However, if you have already cut back on feeding, you can try routinely removing the planaria using a siphon or a planaria trap. This should help drastically reducing the population until it’s manageable.
  • Some people recommend killing them with boiling water or freezing them and disposing them in the trash. It’s important to note that, although it may be tempting, avoid crushing the planaria by hand because since they are asexual, they can reproduce when cut into pieces, which is truly the thing of nightmares!
  • If you want to get rid of all planaria and do so more quickly, medication may be an option. Be sure to always research the product you’re planning to use, though, as many medications are lethal to shrimp! It’s also worth noting that planaria medications can be lethal to both pest snails and ornamental snails, even when it’s shrimp safe.
  • If you’re a shrimp keeper, fenbendazole may be an option. This dewormer is used for many different pet species, including aquarium fish, and many shrimp keepers have reported success when treating planaria.
  • No Planaria is another well-known product that should kill off planaria, as well as the infamous hydra. Although it is advertised as being shrimp safe, keep in mind that some fish are still sensitive to medications! For example, Betta macrostoma, a rare species of wild bettas, doesn’t do well with medications, including No Planaria. If you have sensitive fish, you may want to move them into a different setup when treating the infested aquarium with medications.

When using medications to get rid of planaria, it’s important to remember that the dead worms will all start rotting and producing ammonia within a few hours. An ammonia spike can be lethal to fish, especially shrimp, so keep a very close eye on water values and do a water change if necessary.

How to prevent a planaria infestation

The best way to prevent a future planaria infestation is to reevaluate your regular aquarium cleaning routine. Although it can be a hassle, make siphoning the bottom of your aquarium a regular part of your weekly water changes to prevent excess food buildup.

You don’t have to clean all the substrate at once. For example, you can mentally divide your aquarium into sections and choose just one to siphon with each water change. By doing the tank in sections, you’ll also avoid stirring up too much gunk that can lead to even more ammonia spikes.

Conclusion

There is still much discussion on the best way to eliminate planaria from aquariums. Various fishkeepers report different treatments and outcomes, so a definite “cure” that works in all situations and is 100% safe for all fish and inverts has not been found yet. The treatments listed above should be pretty safe, but unfortunately unexpected deaths may still occur.


If you have any more questions about planaria and the best way to eliminate them or if you want to share your experiences, leave a comment below. Happy fishkeeping! 


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9 Comments

  • Reply George Strampher March 22, 2021 at 3:34 am

    Are the young Planaria these small white objects crawling on the aquarium glass? They aren’t very large only a couple of milimeters, but there are a lot of them. I bought a planaria trap and haven’t checked it for the little buggers yet.
    Thanks

    • Reply Jennifer Doll March 24, 2021 at 4:07 pm

      Hi George!
      There are many ‘small white objects’ that can crawl on the glass of your aquarium, but it’s good that you’re prepared with a trap as Planaria can really devastate an ecosystem. The easiest way you can tell if they’re Planaria or not is by looking for a triangular head. It should kind of look like a stingray.
      As they grow, you should also be able to see the flatness to them, and they’ll be much wider than they are thick.
      If these little creatures don’t have noticeably triangular heads, then it might not be Planaria, though keep an eye out as they start to grow. Some other possibilities are copepods or detritus worms, both of which are generally harmless and actually beneficial to the system.

  • Reply Gabriel December 4, 2020 at 7:33 pm

    Planaria are dangerous. They kill shrimp and can kill young snails.

    • Reply Jennifer Doll December 4, 2020 at 7:54 pm

      Yes! There are many types of planaria, and some are more dangerous than others. In general, it’s best to treat all plants, corals, and other rocks/decorations that you are placing in your tank to prevent an infestation as much as possible. In the event that a planaria slips through, it’s then best to treat the tank even if there doesn’t seem to be any immediate signs of trouble.

  • Reply Phaneendra Hari August 1, 2017 at 9:01 am

    I found that adding a bit of common salt reduced the worms in my tank.. I had an infestation and I have added like 10 table spoons for a 250l tank. Did a water change after a night. Don’t see the worms anymore.

    • Reply Mari August 1, 2017 at 11:27 am

      Thanks for sharing!

  • Reply Gregg Martin March 27, 2016 at 4:18 pm

    Alvin, I don’t know if that is so, wish I could say. But I found a new food NLS Thera +A which contains garlic (and is well made) and the fish go crazy over it. It is said to help keep intestinal parasites from them. The reviews are great, I hope it lives up to the hype. It is somewhat expensive but I see it going a long way.

    Gregg

    • Reply Alvin Yao March 28, 2016 at 9:21 am

      Thx for the reply, however, I had already bought better quality fish pellets which I plan on feeding my fish prior to posting the comment, but thx for the info anyway, might look into it.

  • Reply Alvin Yao February 23, 2016 at 11:20 am

    would cycling a fish tank with fish food cause planaria? I am currently using a bad quality flake I bought a couple of years ago which I decided to stop feeding to my fish.

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