Worms in the aquarium

African cichlid in fish tank
(Last Updated On: March 13, 2017)

Worms in the aquarium. Are they common? Who can get them? What can I do about them? And what do they mean for the health of my fish?

Worms are nocturnal creatures. If you can’t see them during the day it doesn’t mean they’re not present. Because they are light-sensitive, they remain in the darkness of the gravel, rocks, plants or any hideout available during the day or lighting hours.

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Obviously the best way to detect any nocturnal creatures is therefore only at night or when the tank is dark.

It may take several hours after the lights have been turned off and the room darkened before the creatures appear. Using red light will make them visible for the human eye, but will not be recognized by the worms. Rapid movements should be avoided it will scare the worms back into hiding.

Worms grow at a fast rate; the same applies to their reproduction. Once worms have been spotted, and action has been taken to eliminate them, it is this fast rate of growth and reproduction that can be misleading if their successful removal from the tank is believed.

Worms eat everything they can find in the aquarium, which initially makes them appear to be ideal bottom cleaners. Nevertheless the fast growing population makes it a priority to remove all the worms that can be found. Some initially small and harmless looking species can grow to a solid 24-inch sea monster. No matter how long the species will get, there is usually more worm than meets the eye.

Worms can be introduced to the aquarium in various ways, through plants, new fish, fish food, snails etc.

One of the biggest threats for reef and marine set ups are the bristle worms. A fast growing population does not only do damage, but can also lead to attacks on crustaceans, corals and anemones. Bristle worms are visible and can be identified by the many bristles. These worms can grow into 24-inch creatures.

Next to fairly visible worms that are considered non-parasitic, there are of course external and internal parasitic worms that will harm the fish.

Parasitic worms are the roundworm, tapeworm, thorny headed worms, and flukes.

One rule applies, to calm the nerves of the hobbyist; most worms seen outside the fish are usually not internal parasites and not considered as harmful to the fish. Parasitic or harmful worms will not be visible on the gravel or the glass of the aquarium.

Noticing small white worms the size of a few millimeters crawling along the glass are either flat or roundworms. Flat appearances are planaria (flatworms) and the more thin and wiggly ones are nematodes (roundworms). Both of them do not exceed 4-5 millimeters. Both types are harmless to fish and thrive on excessive waste in the water column.

To free the tank of these worms simply do not feed your fish for 3-4 days as they will often feed on them.

The fluke is a parasite worm that is visible on the skin or gills of the fish. Measuring only 0.3 – 0.5 millimeters in length, this oval shaped worm can spread and often result in fish death.

Internal parasitic worms can not easily be diagnosed. Advanced stages can be visible by ulcers on the skin. On the other hand, not all internal worms do pose a threat to the fish.

First signs of internal worms are an increased appetite without weight gain or even weight loss while consuming increased amounts of food.

The tapeworm is the best known though not very common.

Worms of Concern

Anchor Worms

Young anchor worms are free swimming crustaceans that bury themselves into the fish’s skin. It takes several months before the worm becomes visible in form of holes or ulcers on the fish’s body. After laying eggs, the worm dies off.

Since the worm can not be removed by hand, a potassium permanganate bath for about 20 minutes should cure it (dosage 10ml/l).

Thorny Headed Worms

Visible symptoms are white or green threads on the gills. The fish often scratches on objects in the aquarium.

The thorny headed worm is similar to the anchor worm, only smaller in size. It attaches itself to the gills. The cure is also a potassium permanganate bath for 20 minutes (dosage 10ml/l).


The symptoms are mucus covered gills and/or body, red spots on the skin, fins appear eaten away, as well as rapid breathing.

Flukes are flatworms and are similar in appearance as Ick and can be better viewed with detail through a magnifying glass. Flukes will destroy the gills and kill the fish if left untreated.

The best cure is a potassium permanganate bath for 20 minutes (dosage 10ml/l).

Thread Worms

Thread worms are internal fish that sometimes emerge from the fish’s anus. This parasitic infestation can be fatal if not treated in time. Preferred treatment is parachlorometaxylenol soaked fish food and a bath in the same for several days (dosage 10ml/ liter).


These external parasites are visible on the skin, gills and fins of the fish and are similar in appearance to Ick.

Since they attach themselves to the fish, the best method of removal is a bath in a salt solution for 20 minutes (dosage 2.5 % salt to water). During the bath, most of the leeches will simply fall off; the ones remaining can be removed with a pair of tweezers.

Copper sulfate has been used to successfully remove and control less harmful worms. Over time, copper has been found to do more damage than good concerning the overall balance of the aquarium. The side effects of copper are rarely in relation with the possible benefits.

How to build a worm trap

Next to commercially available worm traps, it is fairly easy to make one at home. All that is needed is a plastic container or jar with a lid.

Using a razor blade or sharp knife, the lid is cut in X shape. The corners are then pushed slightly inward to form an opening in the lid. The size of the opening varies, depending on the size of the creatures to be trapped.

For the trap to work properly it is important that the worms do not see the “bait” but rather smell it. The container should therefore not be transparent.

For bait, clam and shrimp meat can be used as well as any fish meat available. The bait should be prepared in a way that is small enough for the worms but just short of being mashed up totally.

The container is then placed in the area where the worms are suspected and kept there over night. Adjustments to the size of the lid opening and the bait source can be made for optimum results.

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146 thoughts on “Worms in the aquarium

  1. Summer says:

    I noticed a hair thin white worm crawling inside my tank on the glass eating a bottom feeder tablet. Im sure it is due to my tank being not cleaned in a while. The problem is my snails had babies and im scared to clean the tank because i dont want to kill all the baby snails the size of bread crumbs so i was waiting as long as i can for them to get bigger i can barley see them now. Is there a way to clean the tank without killing all the snails and are these worms harmful? Any other suggestions?

    • Thilo
      Thilo says:

      Your are correct on the worms, and no they are not harmful. Snails are contributing to the tank problem and less than optimum water quality. Few things to consider; reduce the amount of food, skip a day or two and feed only very little. Perform water changes at 10% every week. Try to add polyester fibers (pillow filler) to your filter, and replace every few days. Once the snails get bigger, you might want to vacuum the gravel as you do water changes.

  2. Samantha says:

    I observed some red round worms while washing my tank. What am i supposed to do?
    Can they be fatal for my fishes ?

    • Thilo
      Thilo says:

      The worms are not harmful, but if they show up in greater numbers it would indicate a water quality issue. These worms feed of decomposing organic matter in the substrate, and these accumulations can cause problems, not the worms, they are just an indicator.

  3. Hannah says:

    Hi! I noticed a very small and wiggly white worm in my tank today. I saw that a usual suggestion for getting rid of the worms is feeding less, but if I don’t want to do this is cleaning the tank more regularly an option? Should scrubbing everything down be able to get rid of them? Thanks!

    • Thilo
      Thilo says:

      The worms can be seen as beneficial as they help to eliminate waste in the substrate. If you are not bothered by a few worms, don’t worry. More cleaning, especially vacuuming the substrate will reduce the worm population. Cleaning the entire tank is overkill, it will cause more stress on the fish than a few worms will.
      Nevertheless, the overfeeding is not just because of the worms. The worms are just a symptom if you will. Overfeeding has other consequences such as a rise in nitrates, possible pH fluctuation as the water harbors more and more waste resulting from the fish food. Not that you have to starve the fish, but reducing the amount of food does not pose any harm.

  4. Amanda says:

    I have a question! So I have hair worms on my tank. No I’m it but on the glass and on my cover. Are they harmful to humans???

    • Thilo
      Thilo says:

      That is generally quite unlikely, but you should always use caution when reaching into an aquarium. Make sure you have no scratches/ open wounds, and wash your arm after you reached into the water.

  5. Erica says:

    I would greatly appreciate some advice. I have a 5 gallon fluval spec V with a betta, sand substrate, and plants. I’ve had a worm population for several months now that I can’t seem to get rid of. They are small white wriggly worms, and my betta does hunt and eat them. I thought they were detritus worms, but they make greenish tube structures on the plant leaves and sometimes the glass, which doesn’t seem to be what detritus worms do. I had driftwood in the tank, but removed it because the tubes proliferated on it. I rinsed the substrate and have been doing multiple water changes every week for a while now. The water quality is better with very little detritus now, and the worm population has gone down, but there’s still a decent number of them. My plants keep dying; I brush the tubes off the leaves but they seem to leave marks and the leaves degrade, so I just can’t get a healthy planted environment going. I’d love some help identifying the worms and how to get rid of them.

  6. Ricky says:

    My pink betta has had difficulty swimming and it is on its side and today I noticed a red spot on the side that is upright so I cleaned her tank and I saw one gray-ish worm in the tank that I have NEVER seen before did the worm infect the fish please help I’ve had my fish for 1 year now and I hope she doesn’t die😢😔

    • Thilo
      Thilo says:

      It is visible, so lee likely a parasite. The worm could be detritus or planaria, both are not harmful, but can indicate poor water conditions. In most cases, if you improve the water conditions, the symptoms on the Betta might be resolved as well.

  7. Dan says:

    I half a 15 gallon column tank planted. I do regular gravel vacs where not carpeted. Lately I’ve noticed and explosion of worms but I can’t seems to find any reference to them anywhere. I had one person at a lfs in the area tell me they are a sign of a healthy tank.

    The are white worms similar to detritus worms but thinner and longer. But they have this encasing tube that’s brown and other shades of brown. The worm will stick itself out like a proboscus and then pull it brownish encasement forward.

    I’d love to send a picture but they are oh so tiny please help

    This is a shrimp tank I don’t feet them other than one shrimp food brick in a petri dish every 6-10 days so over feeding isn’t the issue.

    I just want to know what these things are.

    • Thilo
      Thilo says:

      That would likely be nematodes, check on some images to confirm. Generally not harmful, but if ypu need to eradicate, fenbendazole will do the trick.

  8. Hallie says:

    Help, I have the little white worms, today I found a huge clutch of them on bottom of tank. Where did they come from? No new fish, nothing new, just fresh water when I completely change my tank. Could they have come through our water? I’m freaking cause I don’t know how they got there!

    • Thilo
      Thilo says:

      Detritus worms can exist in the aquarium long before they are noticed. They are not harmful, but will grow at a faster pace when there is more debris/ decomposing organics (fish food/ plant leaves). The population can be controlled/ reduced/ by improving the aquarium maintenance, reducing food, and to make sure that the aquarium is not overstocked.

  9. Ryan says:

    My last batch of blackworms from the lfs had some brown flat worms tagging along. I removed the ones I could find. I’m assuming they’re planaria or maybe small leeches; about 1/4″ long. Would they be harmful to a guppy or shrimp tank? I’ve been feeding them to my festae fry with little hesitation, but I’m concerned about my more delicate species if any remain with the blackworms. Thanks!

    • Thilo
      Thilo says:

      Planaria are not really harmful in general, but that does not apply to shrimp, especially smaller ones can fall prey to some planaria. Fenbendazole will help to get rid of the worms, should they become burdensome.

      If it is leeches, watch for round bite marks on the fish. You should notify your local fish store where you bought the batch of blackworms, they might actually know what worms hitched a ride with your last batch.

  10. Taylor says:

    A few months ago I noticed a thin white worm swimming in my betas fish tank. I cleaned the tank and the worm was gone. Now in the gravel of my tank there is a clump of the little worms. I know that worms that are visible to the human eye are usually not harmful, but is there a way that I can effectively erase these worms from my tank? And what type of worm/parasite could these be, and could they be harmful if it gets too out of control?

    • Thilo
      Thilo says:

      There are options; reduce feeding, use a shipon to vacuum the gravel, build a worm trap, or if all fails, you can consult with your pet store and use chemicals (last resort)

  11. Jenn says:

    I saw an almost transparent looking worm squiggly swimming in my aquarium after I did a gravel vacuum and small water change today. I also saw some smaller ones in the bucket before I emptied it after the second go through with the syphon. Should I be concerned?

    • Thilo
      Thilo says:

      These worms a detritus worms. They feed on dead organic material. They are very common and populate the gravel where most of the decomposing fish food/ waste can be found. You might not have noticed them earlier, but they have been in the gravel for some time. Once the population grows, they can venture outside the gravel and become visible. They are not harmful.
      You can control the worm population by correcting your feeding and maintenance schedule, and by removing the waste from the gravel (siphon). The less decomposing matter, the less worms. Again, these worms are not harmful, some fish use them as snacks.

  12. Mathilda says:

    Hi, I bought the plants for my new fish tank on Saturday and found two small snails on Monday. They’re inoffensive so wasn’t worried, however this morning noticed a load of tiny grey/brown worms on one plant, the rock underneath it, and one worm on the java fern next to it. I suspect the worms and snails came from the same plant. The worms aren’t moving for now, and I still don’t have fish. Would you think they are cause for concern?

    I am happy to email pictures later.

    • Thilo
      Thilo says:

      The snails and worms likely hitched a ride on one or more of the plants. There is generally no concern if the worms are visible. A few worms and or snails are not detrimental but could be if the population is getting out of hand. You can pick out the snails by hand for example if you don’t want to take chances.

  13. Emer says:

    I have a Beta I got in December. I noticed a few weeks in long white stringy poop which I thought indicated a parasite. I treated the water and then he got better. Fast forward a month and it happened again! Treated the water and it seemed better. Three weeks later it shows up again. I follow all proper cleaning instructions, so I wonder where I’m going wrong? The only variable left is the beta food? Any thoughts? I hate to keep treating my tank and fish with antiparasite medicine every few weeks.

    • Thilo
      Thilo says:

      Most internal worms have a life cycle with variuos stages, in case of cammallanus it can be up to 4 weeks. The treatment for parasitic worms needs to be longer than the life cycle of the parasite in order to be successful.

    • Thilo
      Thilo says:

      Free swimming worms are generally harmless, even for snails. What it does indicate is a less then optimal environment for the fish. You might want to increase maintenance, and or control the amount of food.

  14. John says:

    The small white worms in my aquarium aren’t in the water. They are on the flat glass lid, above the waterline. They seem to be eating or living in/on the algae. They usually gather in clusters or rows. My fish seem to be fine. I have removed the lid and scrubbed it several times. No change.

    • Thilo
      Thilo says:

      These are likely larvae, fruit flies, mosquitoes and the like. Both like stagnant water, so increase the water movement at the surface. They are not harmful and often eaten by fish.

  15. Ashley says:

    i have just discovered a weird looking blue worm that moves like a mosquito larvae.. so far i have only seen one in the tank and i also can’t find the name or a image of it on the web
    I’m a bit concerned

    • Thilo
      Thilo says:

      If the worms are visible to the eye, there is little to no concern in general. Stay on the lookout if you see more that just the one. Unfortunately your description is too vague to determine a species.

  16. Lily says:

    I have noticed that in the feeder hole of my aquarium there is pencil tip sized white/cream worm things. They wriggled around on the lid but I haven’t seen them in the tank yet. Just want to know if I should be worried about them. I killed the ones on the lid already btw.

    • Thilo
      Thilo says:

      Could be worms or maybe larvae, especially on the grounds on where you found them. Best way is to remove the feeder and give it good scrub. This should be part of your aquarium maintenance.

  17. Amy says:

    I have a five gallon with a betta and two types of worms. Both stay out during the day when the light is on. The first is super small and is white with partially transparent skin, and a long white line down the body with two dots on either side of the line. They attach to the glass and some are getting a little bit large. The other is long and thin and moves in a caterpillar like motion. There are also super small ones I suspect are babie with round heads and 6 thin legs. Any idea how to remove them? Emptying the tank fully is an option.

    • Thilo
      Thilo says:

      No harm in these worms, they can actually help to keep the aquarium clean by eating debris. The problem is obvious that they do make an appearance if the water is less than optimal. If you have only a few worms, keep the feeding in check and perform regular water changes at 10-15% every other week. While you change the water, use a siphon to vacuum the gravel. Don’t hesitate to dig in a little. This will remove debris, uneaten food, rotting food, decaying organic material etc. This will control and reduce the worm population.

  18. Erin says:

    I have a 10 gal tank with aquatic frogs, tetras, and two plants. I’ve had it for a while now but I just noticed an extreme amount of tiny white worms on the glass. It almost looks like dust because they are so small. I haven’t had any fish die since I first got them as some fish simply don’t survive the stress of being transported. I’ve had a few frogs die from unknown causes. No matter how often I use clarifier my tank is always foggy and has been like this for about 2 weeks now but I noticed the worms today and I have no idea what they are or could be from.

    • Thilo
      Thilo says:

      The fish/frog losses might be directly related to what causes the worms to grow in high numbers. Worms thrive in nutrient rich environments. You have detrius worms, worms that feed of organic waste. You might want to cut back on feeding and increase your maintenance routine. Water changes at 10-15% every other week while vacuuming the gravel. Make sure your plants have the correct light and substrate. If plants do not flourish, they contribute to aquarium water quality issues.

  19. Kristen says:

    So, very small white worms on glass. Look to be flat Planaria but are too small to completely identify. However….I know for an act they aren’t detritus worms as I’ve had fish deaths in different tanks as well as these things attacking nerite snails. (They came in on some plants I didn’t treat.) Anyway, these things chased nerite snails out of the water. I was attempting to treat the tank so removed the snails to a clean tote filled with clean water. The snails didn’t act right still and when I looked closer there were a bunch of these things in the tote. One snail ended up dead.

    Anyway, back to now, I have a 10 gallon tank with one bristlenose pleco. When I first got him, he came with a sibling. That sibling died and I noticed an outbreak of these. I thought I had gotten rid of them but no, they still hung around. I will need to move this fish but these things transfer very easily. Any idea on what they are and how to get rid of them? Water parameters are perfect and tank is not overfed. They seem worse now after huge water change and treatments of prazipro. I’ve also tried general cure and no Planaria. No luck. Any other ideas?

    • Thilo
      Thilo says:

      I would definitely give a worm trap a chance to reduce the population. If you suspect an internal parasite, a bath would be preferred instead of a general in aquarium treatment.

      • Kristen says:

        I don’t think a worm trap would be effective for these. They are way too small. So they wouldn’t stay trapped. I don’t think I’ve seen them leave the glass but then again, as small as they are, I doubt I would see them on the sand. I don’t think it’s internal that I can tell. The pleco looks fine to me.

  20. Jessica says:

    I was putting a cucumber down for my pleclo and a worm poped out for like ten second. It was small,white,swam like a s,and was flat but a bit round. My fish haven’t died. No ulcers. So no internals. And I haven’t seen others. So is this working. Harmless. Will he hurt my pleclo.

    • Thilo
      Thilo says:

      No harm comes from theses worms, but they do want to tell you to increase the maintenance a little to reduce the mulm and debris in the gravel, otherwise the population will increase. You can quickly build a worm trap and help reduce the population, just type worm trap in the search window above.

  21. Joshua M Teixeira says:

    I have a 3gal freshwater tank with guppies. I tried to make it a Natura tank with equilibrium so only maintenance is feeding and adding water. Guppies are not the best fish for this. Well some sort of parasite kills fish every so often but it has got in my hand through fingernails anytime I touch any of the water. Kind of look like hookworms under skin. Very hard and crunchy, blackish appearing and very hard and painful to remove. Bleeds a lot. What kind of worm is it?

    • Thilo
      Thilo says:

      There are some conflicting info so it is not conclusive to diagnose. It could be Anchor Worms, but lets not make this certain. In any case I would recommend a commercial de-wormer that addresses parasites.

  22. Kristinia says:

    I have these weird white little worm like things hanging on the walls on my 10 gallon fish tank I don’t know if it’s worms or what, 2 of my fish randomly disappeared and I hope they had nothing to do about it, when I look at them closely, they kinda move with the water like in a “S” shape but I am not sure. Help! There also on some of my decorations in the tank, they are gross :(((

    • Thilo
      Thilo says:

      Nematodes, they are harmless. Relatively harmless, because they populate tanks with sub optimal water conditions. Decaying plants, mulm, overfeeding etc. contribute to the increase in numbers. Besides an increased maintenance schedule, you can build a worm trap to expedite the removal.

  23. Melody says:

    I have a small freshwater tank with tetras and when I clean it there are thin red works just a few mm long that come out of the substrate. I also have an albino cleaner who seems to have a deformity in the stomach area and I am worried it has parasites. What should I do?

    • Thilo
      Thilo says:

      The albino could be quarantined to make sure others are not affected if the fish carries a parasite. You can treat the fish in the quarantine tank. At the same time remove as many of the worms you can detect and keep a close eye on the others. It will also clean your gravel as the worms are likely detrius worms thriving on waste collected in the substrate.

  24. Jacob says:

    I’m having some issues in one of my fresh water tanks. I’m seeing 3 different types of creatures both free swimming and attached to the glass. 1 is a white tiny looking worm free swimming in the water and sometimes I do see them on the glass. I do suspect these to be detritus worms. 2 seems to be some sort of white flat worm moving across the glass, I’m not sure if it’s planaria bec I can’t tell if it has a triangle shaped head or not. I’ve read and seen a few vids saying that planaria can be harmful to fish. 3 is more round and white. If looked at very closely they do have black in the middle. I was able to pull out the 3rd ones and inspect them and they seem to have a hard outer shell around them. Might be some sort of very small snail but im not sure. Ive missed a few water changes on this tank and I’m deeply regretting that now. If you can help me I would really appreciate it. Thank you very much for the article.

    • Thilo
      Thilo says:

      I think the best recommendation would be to reduce the amount of fish food and to start vacuuming the gravel during water changes. A worm trap might speed things up. There is no magic solution to the issue.

  25. Aidan says:

    I have these small black worms that are crawling on my glass and in the water in my turtle tank I don’t know what they are and how to get rid of them they are small in size about 5 mm and are black with gray undersides and sometimes they have a upside down Y look to there shape

    • Thilo
      Thilo says:

      Black worms are likely insect larvae, mosquito, moth fly etc. They pose no harm to the turtles, but they will eventually get their wings.The best way to get rid of them is to fish them out as you spot them, or clean the tank and refill it with fresh water. Make sure your filter is clean and working, the filter outlet should create waves.

  26. christopher says:

    Hi I have these tiny red worms developed my freshwater fish aquariumi Had problem before and use to be able to get a product from pet supermarket they were a tablet form that fizzled and had got rid of the problem now i cant find the product anywhere now,is there something else i can put in my tank that will not harm are fish,alls they carry now is stuff to kill the ick parasite.please help me out Thanks.

    • Thilo
      Thilo says:

      Tiny red worms could be a harmless variety especially if you see them in the substrate or open water. The worm of concern is Camallanus. This is an internal parasite and visible at times by emerging from the fish anus. Similar to ick, the parasite has a cycle. Larvae is settling on the substrate and molts into the next stages using intermediate hosts. Camallanus does need a host to grow and most need an intermediate host, but some can skip the intermediate host and grow and molt directly within the fish’ stomach. Once grown to a full size adult, the cycle begins anew by Camallanus producing larvae leaving the fish (host) as the fish defecates. This takes just a few short weeks (depending on the environment, temperature etc).
      In this case you need to look for a mediation that targets internal parasites. As always, makes sure to improve your water quality, it is the best prevention.

  27. Emma says:

    I only have a 10g and I know that clown loachs get really big, but I do have a bigger tank for them to go into once they get bigger like 70g, but would a 10g be okay for a couple of babies just for a few months to clear out the worms if they would help????

    • Thilo
      Thilo says:

      No need to wait, if you have a 70 Gallon aquarium, use it. Especially if you are planning to use it later on anyways.
      Technically, yes you could have them as babies in the 10 Gallon setup, but again, if you switch them to a larger aquarium anyways, you can save yourself time and efforts in using the readily available 70 Gallon aquarium right from the start.

  28. Emma says:

    Hi just wondering I have some very tiny worms that float around the tank and on the glass( they are white) And I had did research on them and it said that they were detrisus worms and I was just wondering if this is true and it also said that if you kill them with chemicals or medicines to get rid of them that they would die and they would become a toxic from so many of them dying. I have been told that getting Clown Loachs can help get rid of them, Is this true.

    • Thilo
      Thilo says:

      You are likely correct, and the best way to remove the worms would be a worm trap and to reduce the amount of waste that the worms feed of. No need to hurry into anything as these worms pose no harm to the fish at all. Some fish do eat these worms, stop feeding the fish and see if yours are worm connoisseurs.

  29. Jess says:

    Hi, wondering if any one can help, I’ve just noticed little brown worm type things in my 70 liter tropical tank. Are these harmful and how do I get rid of them? Thank you 🙂

    • Scott @ Algone
      Scott @ Algone says:

      Small brown worms in the aquarium usually are planaria. They can thrive in aquariums with poor water conditions often due to overfeeding and the resulting excess organic waste in the tank. Please talk to your local fish store pro for treatment options, and also be sure to describe the worms again to assure correct identification.

  30. Lucie says:

    I have a betta fish and a mystery snail, and I was cleaning their tank when I noticed this tiny white worm about 5mm long, and it was wiggling around. Now my snail is dead! Is it dangerous? I got the snail about 2 months ago, and the betta fish about 1 year ago.

    • Thilo
      Thilo says:

      You will likely find more of these worms. Turn off the lights for a few hours and take a black light to the aquarium. These worms are not harmful, you can increase maintenance, siphon out the gravel during water changes, and reduce the fish food. It is coincidence that the snail died while you discover the worm(s). Look at the shell of the snail to see if you can see deformations or any other signs that will assist you to determine what happened.

  31. Hasitha says:

    Hi, I changed all my fish to a pond. The aquarium I previously used started having worms ( the aquarium was not cleaned after I moved the fish ). Can these worms be used as fish food ? Are they harmful?..

  32. Marina says:

    Hi there,

    I’ve been having trouble with my betta fish over the past few days, and my internet searches have just left me more worried and confused than when I began. About a week ago I noticed his poop attached to his body, and a long, white-coloured one. Eventually it fell off as normal, but the same white poop occurred once again a couple days after. Now four days ago, I noticed he had developed quite a large bloated stomach/abdomen, and he wasn’t pooping anymore. I assumed he had been overfed, so we fasted for three days. I also gave him a small piece of a cooked pea, however he still didn’t poop at all (that I could see, and it’s usually very obvious).

    Today, I gave him a couple of his usual pellets, which he was very grateful for- but still no poop. So I put a mirror in front of him, and he let out a tiny brown nugget! I was really happy to see that. The abdomen is still huge, especially on the right side. There is no clear pine-coning, and he does not have any swimming issues (aside from mostly sitting at the bottom of the tank of late). I have also just noticed tiny white worms on the glass of the tank, it seems like they are hatching from tiny black eggs (too small for me to see though). There was one worm floating around the tank and just as I wanted to grab it out, my betta ate it!! Have checked water conditions, and all (ammonia, nitrate, nitrite & PH) are very normal.

    I guess I’m writing because I hope someone can help with a diagnosis. I really want him to survive this, but I don’t know what to do about his bloated tummy. It seems like it might just burst eventually.

    Very sorry for the long message. Hope to hear from you soon.

    • Thilo
      Thilo says:

      The bloated belly could be constipation. Stop feeding the fish for two to three days, then feed the inside of a pea or some daphnia. This could already make a difference. White poop could be the sign of an internal parasite, if the first option isn’t working, look into applying medication addressing internal parasites.

  33. Joachim says:

    Hi, are there any worms that are benefitial composters that will improve substrate conditions for plants without being a hazard to the other tank inhabitants. I.e. in your garden regular worms improve the soil. Any aquarium equivalents?

    • Thilo
      Thilo says:

      Pretty much any of the harmless worms can have beneficial characteristics. The detritus worm is breaking down waste for example. You will find worms in many aquariums, most reside unseen. It generally becomes an issue only when the worms are overpopulated. Not necessarily because of the worms, but is is a sign that the aquarium is less than optimal maintained.

  34. Veronica Burlison says:

    Hey there. I have very tiny tiny whitish worms on the water surface in my aquarium. About 1mm in length. It’s a 10 gallon with 1 betta male and 1 nerite snail. If you didn’t really look for them you wouldn’t see them. Any idea what they could be? The tank was cycled with pre existing media for 2 1/2 weeks and then bio starter when I put them in the tank. They are also in my 3.5 gallon with another betta.

    • Thilo
      Thilo says:

      These re likely planaria or detrius worms. Nothing to worry about.
      Reduce the amount of fish food and feed every other day. Replace 20% of the water per week using a siphon to clean the substrate. Continue until you no longer see the worms.

  35. Thrasher says:

    I have tiny thread-like worms in my fish tank. I was told they’re called enimas. But no one can tell me how to get rid of them.

    • Thilo
      Thilo says:

      In most cases when you can see worms crawling about, the issue can be remedied with a few simple steps. First, address any pressure points such as overfeeding and non optimal water conditions. Use a siphon to vacuum the gravel. Stop feeding the fish, or limit the food to whatever they can eat in just under one minute and feed every other day, fish might just turn on the worms for dinner. Build a worm trap. Zucchini on a fork, wait until populated and remove.
      If you see changes in the fish, especially bloating, inflammation, lack of appetite, ulcers, nodules, lumps etc, you will have to treat for internal/ parasitic worms.
      Assuming you mean annelids, these are detritus worms and absolutely harmless.

  36. Sarina says:

    I have little worms in my 10 gallon that swim like snakes in the open water, there about 2mm-2cm long each. I’m afraid they are nematodes or parasitic. I also have little ovals moving on the side of the tank that are about a millimetre long each. I don’t know if they are harmful to my fish, or how to get rid of them. I have an amazon Puffer with stripes, and the temperature is about 80 degrees. What should I do?

    I noticed the ones that swam out in the ocean about a month ago, but my Puffer is fine so far. But I just noticed the ones on the glass just last night.

    There’s also 2 spots in my tank on the rocks that are about an inch each that has bright green algae. Should I use my vacuum and suck it up?

    • Thilo
      Thilo says:

      These are more likely detritus worms, but inspect your fish, if they show any signs of a bloated abdomen. Keep in mind, worms that you can see are harmless, parasites life within the fish and the first sign would be a fish behaving abnormal in combination with obvious symptoms of illness.
      Good husbandry, water changes, less feeding and a worm trap will be the way to go.

  37. Pyra says:

    I recently found these tiny worm like things moving around the bottom of my tank and they seem to be eating the algae tablet I put in the tank for my snails. Just a few days ago my mystery snail laid eggs at the top of the tank. Today I found the tiny worms around the snail’s eggs. What kind of creature is this and is it harmful to the snail eggs?

    • Thilo
      Thilo says:

      Worms eat anything including snail eggs. I think it is time for a worm trap (see above). If you plan on keeping the snail eggs, you can use a tank divider until the snails are hatching and become too big for the worms.

    • Sinchan says:

      Me too , I have three mystery snails in my tank the adult one laid eggs today and I found two long worm things going around the eggs what do I do???

  38. JD says:

    Not a question, just a thanks for running this site. Generally when I have a problem all I can find on my searches are forums of fish owners with dubious experience that never have consistent answers among them (i.e. is this harmful, what is this, this is how you get rid of it). I have found your site looking into tiny, white slugs that have appeared on my tank glass and I wasn’t sure what they were. Now I know and am taking steps to get rid of them (mostly cutting back on feeding with water changes, I’m terrible about over feeding). So thank you for running this site and it’s being added to my bookmarks for future reference.

  39. Vann says:

    I have prepped a new tank and used old filters to cycle. It has been about a month and now I have this greenish gray matter on the bottom that appeared in the last two weeks. Is is not stuck and easily removed, except it comes back and under a microscope slide I have found Stylaria and other diatoms. I think this may have been a turtle tank previously.

    Anyway, I want to move my juvenile angels I raised from fry to this tank. I have read that they are harmless and the angels will eat them. Is this true?

    I did not notice any rotifers in the samples, but did notice some copepods and ciliates.

    • Thilo
      Thilo says:

      Yes they are harmless and are likely being eaten by the angels. The grayish matter is mold/ fungus. You might consider increasing water circulation and some corrective measures getting the excess nutrients out of your aquarium. This is best addressed now because it will fuel excessive age growth next.

  40. Jelena says:

    Hey I have these worms in my tank, but they dont look like any of the ones describer here. They have a round head and a slim body, they hang at the top of the water they’re about 5mm long and wiggle they’re tails to swim to the top, im afaid to put my fish back in the water.

    • Thilo
      Thilo says:

      Might be planaria, either way they are harmless. Use a worm trap (attach string to a fork add some zucchini and wait for the worms to take the bait/ the string is for easier retrieval of the fork).
      Increase maintenance, vacuuming the gravel each time water is changed. Reduce the feeding to once a day every other day. This will do the trick, then maintain a healthy aquarium to prevent any less optimal conditions which will favor worms and other issues.
      If you are impatient of need a quick fix, you can use fenbendazole a traditional de-wormer. Use as directed.

  41. Ciara says:

    Hey, I’m still kind of new to the whole aquarium thing. A few months ago I noticed these very small white worms sloshing around if the gravel in my tank was disturbed. I changed the gravel out and washed everything down, but a few weeks later, I saw them come back again. I’ve changed out the gravel and everything in the tank about 4 times now. They keep coming back and I don’t know why or what I need to do to get rid of them permanently. Please, any advice is appreciated.

    • Thilo
      Thilo says:

      The easiest way to get rid of the worms is to reduce the feeding to once every other day. Just feed what the fish can eat within one minute. Worms thrive on uneaten food. Make sure to vacuum the gravel during you regular scheduled water changes.
      In addition, use a piece of zucchini to attract the worms (attach to a fork, tie the fork to a string) the pull them out with the “bait”.

  42. Ashanti says:

    okay so i just got my fish today and everything i put in the 3.5 gallon tank is new but my sister and i went down to the creek by my house and got some rocks so we took some of them home and washed them with a tooth brush and warm water and then we set up the tank and just now i was looking at the tank and i see a small thin kinda white worm just swimming around so i freak and i get some water from the tank and i but my better fish in it and now i don’t know what to do plz help

      • Ashanti says:

        the worm is about a cm long maybe smaller i don’t know its whiteish and like its body goes up and down when it swims is it harmful to my fish? how can i get rid of them??

    • Thilo
      Thilo says:

      Okay, your tank is brand new, so there is no issue to remove everything and fill it back up with water. It is likely that the worm hijacked its way to the aquarium on one of the stones you collected. Generally, it helps to keep these stones soaked for a while in a separate container before adding them as decor. Please feel free to read about new setups and cycling an aquarium on this site.

  43. Wendy Young says:

    I have a cichlid that seems to have red worm like things on its gills. Resembles anemone more then anything. Also has ich treated with kordon rapid cure. Malachite green main ingredient. Seems to have cleared one side but still on the other. Should I isolate the fish? Is there a different solution I should try?

    • Thilo
      Thilo says:

      It definitely is parasitic and it will impact the other fish. You can try a potassium permanganate bath which will cure the problem. Do keep an eye out for the other fish to see if they show symptoms. Malachite green works as well, especially if you decide to treat the entire aquarium. A good maintenance session in-between treatments might be advisable.It will help in the long run, keeping in mind that fluke eggs hatch within 3 weeks, so the treatment needs to be extended accordingly. Make sure the tank is well aerated during the period of treatment.

  44. Saniya says:

    My fish give birth to baby fishes and then suddenly i saw many red worms inside my tank..how come they get inside it and what should i do to get rid of them and are they harmful for my fishes??

    • Thilo
      Thilo says:

      If you can see the worms and if the worms are not attached to a fish, they are non parasitic and quite harmless. The worms you see thrive on water with high nutrients. In most cases you have worms in the tank without knowing. The numbers are small and you usually do not detect them until they start reproducing if the water becomes high in nutrients.
      To solve the problem, reduce the fish food significantly and feed only every other day. Most fish eat these worms. Increase, or adjust your maintenance routine and or use bait (zucchini on a fork) to attract and remove the worms.

  45. Sarah says:

    Hi I just noticed these really tiny gray worms with a little black at the end type worms in my turtles tank. There probably are hundreds of them! Should I remove him? Will they harm him? How do I get rid of these?!

    • Thilo
      Thilo says:

      Detrius worms cause no harm to a turtle. These worms are actually quite common in turtle tanks because of the amount of food and amount of waste created in consequence. You should start vacuuming the gravel, which will remove most of the waste. Fish do no tolerate chlorine, but turtles can tolerate tap water treated with chlorine. This is a quick way to rid the worms as they do not take chlorine well at all.

  46. Mauro II says:

    There is a white very very tiny like worm wiggling in my aquarium. All my goldfish died because of Whitre Spot, and I treat them and it goes away but after a day they got fin rot instead. There is a dead fish day by day. Is the tiny worm harmful when I put new fish? your answers will be a big help for the crisis I am facing right now.

    • Thilo
      Thilo says:

      “White Spot” disease is generally known as Ick and is a parasitic disease. The life stages of this parasite spans about one week. The stages include a feeding and reproductive stage. You can read all about the details right here, just tape Ick into the search box on the top right of this page. You need to eradicate the parasite and treat your aquarium with medication immediately or you will lose all your fish.

  47. Albert says:

    I have about a billion very very tiny little white worms all over my tank floting around in the water and on everything. What are they and how do i get rid of them?

    • Thilo
      Thilo says:

      Yes, these are detrius worms. Please see detailed answer just below. Improving water quality is the key. These worms are harmless, but a sign for a less than optimal aquatic environment.

  48. Veronica says:

    I have no fishes in my tank for a while but there is still water, some tiny brown things swim around it and I put nothing in the tank, they’re as small as the top of a pencil led what are they ?

    • Thilo
      Thilo says:

      These are likely detritus worms, harmless and actually beneficial in reasonable numbers. These worms help break down waste (same as earthworms). They populate the gravel and are rarely seen outside their habitat. Reasons for them to wash out into the water column is explosive growths due to accumulating waste/ detritus or the lack of oxygen, both are somewhat related obviously.
      Fish will eat these worms and an increase in maintenance will control the worms without issues.

  49. Lochlan.Whaites says:

    My comet has 2 to 3 white worm like objects coming from the inside of the gill (1 gill) that go outside and back in when the fish breathes. The surronding area is red and looks inflamed. The gill that has the worm like objects is bigger than the other gill and unable to close fully.
    It rubs this gill on the side of the fish tank.
    No new fish have been introduced for 8 months and the food hasn’t changed in 2 months.

    • thilo
      thilo says:

      It definitely could be a parasite and should be treated. We do not diagnose via email, but it could be either gill flukes, anchor or thorny headed worms. In either case, and in general, a potassium permanganate (10ml per liter) for 20 minutes will provide a likely solution. Keep a close eye on the progress, but especially the other fish, anchor of fluke worms can show on other parts of the fish. Look for red points and ulcers.

  50. Jamie says:

    I had some gravel that was in abother tank for about 1 and a half months and it had maggots what should I do get new gravel or clean it

    • Scott @ Algone
      Scott @ Algone says:

      You can rinse it thoroughly and then boil it. That should take care of any potential residuals. Just don’t use any soaps or cleaners, fresh water only.

  51. Madison Andrews says:

    Hi i have a betta fish and i had to take him out of his tank because he has fin rot… Well, i can now see many tiny little brown worms swimming around in the vacant tank. These worms are about as big around as a hair and about a centimeter in lenght. Do you know what they are and if so are they dangerous?

    • Thilo @ Algone
      Thilo @ Algone says:

      The worms are completely harmless, but indicate a few issues with one or more of the following:
      high bio load/ too much food/ insufficient filtration/ lack of filter maintenance/ general maintenance (gravel vacuum) water changes

      These worms strive on high amounts of decomposing organics (mulm) the more detritus the more worms there will be. If you correct and improve the water quality, the worms will disappear. Water quality is also the main trigger for fin rot.

    • Scott @ Algone
      Scott @ Algone says:

      Take pictures of the fish or describe the condition as good as you can to your local aquarium store. They should be able to recommend and sell you the correct medication in order to treat the fish. Just make sure you pick a store with knowledgeable staff.

  52. Margaret Karinen says:

    HI, I have Garra rufa. A few days after I got them, some of them died and had these holes in their stomachs or close to the stomach area. I also noticed some little white worms on the bottom of the tank. It looked to me like the worms came out of pods. I am not sure. For about 5 days no more fish died, then yesterday 4 more died and I notice the hole in them. Does this sound like the ‘Pod worms’ are killing my fish? if so, is there something to deworm them? Thank you

    • Thilo @ Algone
      Thilo @ Algone says:

      It is quite likely that the worms are parasitic. You will need to treat the fish. There are several products available such as “Parasite Guard”. Follow the instructions and repeat treatment after about 2 weeks as some parasites have longer life cycles.

  53. Phillip baltzer says:

    I noticed little brown worms the size of pencil lead tips on the inside glass of one of my aquariums. is this dangerous to fish and how do I get rid of them

    • Thilo @ Algone
      Thilo @ Algone says:

      Out of the most common worms, roundworms (long and thin) are mainly whitish, annelids (cylindrical body) pinkish red, and flatworms (triangular head/ flat body) best described as mostly brown/ gray in majority. Best guess, these are detritus worms.
      Detritus worms are not harmful to fish and their food source consists of united fish food, decaying organic materials.

      These worms are best collected using a worm trap. You should also adjust your aquarium maintenance schedule if the worm issues persist. Avoid overfeeding and detritus in the gravel.

  54. Carmen says:

    Hi I recently found the free swimming white worms in my tank and I am a beginner fish keeper and I freaked out when I saw them. I have one male betta fish in my tank and it seems like he likes snacking on them.
    However what i am concerned with is whether it is harmful to humans? I did some reading and it said that these worms are nematodes or roundworms? I’m just super worried because sometimes when i clean the tank, i spill or sprinkle a bit of water on my desk (my tank is on my desk) and i just wipe it away with tissue and sometimes I wipe my eyes with the back of my palm after cleaning the tank (without washing hands yet).

    • Scott @ Algone
      Scott @ Algone says:

      Hello Carmen, sensible precautions are always recommended. While there isn’t generally a problem, it’s always a good idea to wear rubber gloves when reaching into the fish tank and thoroughly washing your hands when aquarium maintenance is complete. If you spill some water be sure to wipe it up immediately and use soap and a disinfectant if you are concerned about any parasites. Just take sure you don’t contaminate the aquarium with any soaps or disinfectants. I wouldn’t be too alarmed, but at the same why not avoid the risk of any contamination by taking appropriate precautions, no matter how remote the possibility.

    • Scott @ Algone
      Scott @ Algone says:

      These worms/parasites are generally harmless to humans. Nevertheless it’s always a good idea to wash your hands after reaching into the aquarium. You could also use long sleeved rubber gloves.

  55. Brittany says:

    I have a 30 gallon tank with 2 snails and a 3 inch suckerfish along with a few other tiny fish. The tank was set up 2 days ago with clean water new gravel and now I’m seeing clear/ white worms that range from centimeter long to about 3 inches and are rapidly producing. What might they be and how can I get rid of them? The longest one I’ve seen is about 3 inches and has attached itself to my baby suckerfish.

    • Thilo @ Algone
      Thilo @ Algone says:

      With the tank being only 2 days old, the worms might have been imported by either the, decor, substrate, plants etc. In this case I would recommend starting over making sure the setup is free of worms from the beginning. Please observe your fish closely and make sure they are not harboring worms. You might have to treat the fish first if you notice any signs. Generally, if you see the worm outside, they are not likely harmful.

  56. Krystle says:

    I have had tiny white/clear worms on the glass if my freshwater tank for a few months now. I have done vacuuming and water changes and treated my tank with copper power green which was recommended to me by a pet store. Nothing has helped and they keep coming back. How do I get rid of them? Is there something I can treat my tank with? I believe they are either planaria or detritus worms I’m not 100% sure.

    • Thilo @ Algone
      Thilo @ Algone says:


      Copper can easily be overdosed causing issues that massively outweigh any benefits. It can hurt the beneficial bacteria. Vacuuming the gravel and performing regular water changes are positive. You should now reduce the feeding of the fish to whatever they can eat within just under one minute. Feed only every other day. In the long term, this will reduce the available waste on which these worms feed of. Reducing the food will also entice some fish to look for a food alternative. You get the idea …

      • Ree says:

        Hi. I am desperate to find out what these thin white thread like things are in my freshwater tank. When I put the light on, they appear to rise to the top of the tank. They look like white inch worms. They swim. I have already lost a few fish and now have a loach who is rubbing himself on the rocks at the bottom of the tank. He is bloody red on both sides and his gills have small red splotches. I know that he is in distress. I have dosed the tank with copper green and twice with parasite guard. If you could give me your opinion of the problem, I would be greatly appreciative.

        • Ree says:

          Hi. New development. I replaced the heater with a stronger model. Turning heat up gradually to 80 degrees. The pleco is now attaching itself to the loach and cleaning the wounds on its sides. Is this harmful to either fish?

          • Thilo @ Algone
            Thilo @ Algone says:

            Pleco’s are territorial and can be aggressive. Despite these fish being sold as “algae eaters” pleco’s are actually omnivores. The attaching is not a friendly move, you need to separate the fish.

  57. Cynthia says:

    Hello this is the second time that I notice white clear tiny worms floating and attached to the tank. The first time my fish died and had blood when I took him out the tank. is there a way k can treat the fresh water fish or water? The fish is a beta.

    • Thilo @ Algone
      Thilo @ Algone says:

      The free floating worms are likely planaria and not really harmful. Anchor worms are external parasites, you will spot them being attached at the fish. In both cases, it helps to increase aquarium maintenance and to reduce the amount of food. This certainly helps with planaria as the populations grows with excess organic material. Reducing these factors will reduce the population.

      In case of anchor worms (or other parasitic worms), it would be advisable to use some medication eliminating the parasite. Keep in mind that the worms and the fish death might not be related, but if in doubt, I would treat the aquarium to eliminate all traces.

  58. Claire S says:

    How do I get rid of spaghetti worms in my reef rank? They are keeping the zoas closed with their fine hairs.
    I have many fish. Some one said a 6 line wrasse would eat them but no luck. Please help!!!

    • Thilo @ Algone
      Thilo @ Algone says:

      Terebellids known as Spaghetti worms among aquarists are actually quite beneficial. These worms are detritus eaters and keep things clean in the aquarium. Generally the population is non threatening, but as the detritus increases, so do the numbers of worms. The best way to control them is to improve the environment. The less detritus the lower the worm population. A natural enemy would be the sand sifting star.

  59. Thilo @ Algone
    Thilo @ Algone says:

    Planaria worms seem to be the most likely as they are known to eat worms. These are not harmful to fish, but do indicate a less favorable aquatic environment. Blue Mystery, or Apple Snails, do prefer a nutrient rich environment. You should control the number of snails in the aquarium. As beautiful as they are, too many of them will end up being a pest.

  60. Adam says:

    Hello I have a ten gallon aquarium an my blue mystery snail just laid eggs I noticed a couple days later that one of them had a worm poking into one of the eggs wich are above the water line I removed it and the next day I found more of these little worms with brown/black color heads… can some one please help with info about these worms as far as how to remove them or if they are harmful to my fish aswell or are they only after the snail eggs

  61. Cory says:

    Our fish recently died, it started out with nasty aquarium water & the fish had red spots. It turned into looking as it scum was eating away at the fish. Now that he’s dead I’ve noticed small brown worms at the bottom of the tank. Which kind of worms are these? Could this have been what killed my fish, I tried amoxicillin but how do I make my tank safe again?

    • Thilo @ Algone
      Thilo @ Algone says:

      It is possible, but he worms are very likely not posing any danger to the fish, unless you detected them on the fish. Small brown worms could be planaria and or if you have excess mulm in the gravel, detritus worms. Both are harmless. Deteriorating water causes stress on the fish and increased stress levels reduce the slime coat. Without this protective shield, the fish gets vulnerable. Red spots could be inflammations caused by the less than optimal water conditions. First on the agenda should be to make the water safe for the fish again. This generally solves quite a number of problems.

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