Any aquarium hobbyist that has noticed tiny white worms in their fish tank likely has one of two issues they to address. The more common worm, the Detritus Worm, is naturally found in many aquariums, and any overpopulation can be fixed with proper maintenance. The less common Planaria worms are a more complex problem.
Before making any changes to your tank, be positive about which white worm you're dealing with. Only then can you know if the careful use of a de-wormer or just a good cleaning is what is required. Misinformation about the correct use of de-wormers and overuse of de-wormers often leads to harming and killing of fish by mistake.
Detritus Worms are annelid worms; this is the phylum that includes the segmented worms such as earthworms and leeches. They look like thin, pointy, white-brown strings that wiggle through the water and between pebbles. Detritus Worms are detritivores, meaning that they only eat decomposing plant and animal waste material; they will not harm your fish.
It is not uncommon for an aquarium to have detritus worms, as they can be introduced through a variety of means. For instance, they may have come in with a new fish or plant, and may even have been present in any gravel swapped in from another tank.
Quite often, detritus worms are not even seen. They tend to live in between the pebbles of gravel where they eat the debris left over from feeding or deposited by your fish. You may only notice them when they get sucked into a tank cleaning vacuum. detritus worms may actually be a beneficial symbiotic organism in your tank system as they help to keep your tank clean.
Removing Overpopulated Detritus Worms
When you see detritus worms coming out of the gravel frequently, that means that a problem has occurred in your tank. It can be shocking when your normally clean water becomes filled with hundreds, if not thousands, of tiny white worms, especially if you don't know what caused the bloom. But it is important to not treat a detritus worm issue with de-wormers or any medications; these will not take care of the problem and may cause an inadvertent fish kill.
An overabundance of annelid worms can occur when tank maintenance has been lacking. Insufficient cleaning schedules or overfeeding of fish can cause detritus worms to reproduce rapidly and get out of control. Reduced dissolved oxygen or pH levels that are too low (both are symptoms of unclean water) will cause detritus worms to seek more oxygen. The worms will flee their gravel home, traveling up the water column toward the surface.
Worm removal begins by giving your tank a thorough cleaning. Use a gravel vacuum and change the water to remove the majority of the detritus worms and also their food sources. Secondly, be sure to check your filtration system for any issues. As a proper oxygen level is required to keep worms at bay, a well-maintained filtering system is essential to their prevention.
Going forward, regularly clean the substrate, review your feeding practice, and assure that your tank is not overstocked with fish. Ensure that they are getting enough proper food without creating too much waste.
Planaria (singular, planarian) worms are not as common as detritus worms, but they are much harder to remove. These are flatworms; most are brought in with pond plants, especially if acquired from a local pond or natural water source. If you've introduced those recently and then noticed white worms, chemical treatment is required.
Planaria are flatworms in the class Turbellaria; they are found in both freshwater and saltwater environments the world over. They are quite small, but if you can examine them closely enough, you'll see eyespots as well as protrusions on both sides of their widened heads. Quite often, these are the worms that are crawling across the glass inside an aquarium.
They are related to flukes and tapeworms but are evolutionarily more ancient than the Annelid Worms (which are not "flat" worms). These ancient worms are asexual animals, meaning they can reproduce without mating. Even after cutting one into pieces, you'll have a new worm for each piece.
What makes these worms problematic is that they are both scavengers and carnivores. Although they will not harm your healthy fish, they love to feast on fish eggs and therefore are dangerous if you are breeding egg-laying fish. They may also prey on gills and eyes of weakened adults.
If you do indeed have a planaria problem, it's a serious issue. While detritus worms can number in the thousands, Planaria troubles are often caused by just a few flatworms that are difficult to locate. This is why getting rid of planaria requires chemical treatments. But as chemicals may also harm your fish population, you'll want to be absolutely sure of the presence of planaria before seeking the solution.
Thoroughly research each of the following chemical products before using them to predetermine if they will be safe for your species of fish. Vulnerable invertebrate species like snails and shrimp should be removed. Sharks, silverfish, lionfish, piranhas, bottom feeders, and certain scaleless or Metynnis fishes may also be sensitive to some worm eradication treatments. Any worms on these tank residents must be removed manually with blunt tweezers or a quick salt or freshwater dip.
With all de-wormers, be sure to use the precise recommended dosage from the manufacturer. Too much can cause a fish kill. Also, these products require strict adherence to safe handling instructions. The recommended de-wormers for killing Planaria include:
- AAP Clout Parasite Treatment (or any product containing Trichlorfon) is a neurotoxin and this seems to be the most effective.
- API General Cure may be less effective but is an alternative to Clout.
- Levamisole HCI is a general de-wormer, though it should be used with caution and may not be as effective as other options.
All of these products can be found at American Aquarium Products, which also has information about their safe handling and application.
Vladimir Orobets et al 2019. Control of fish parasites in aquaculture.
IOP Conf. Series.: Earth and Environmental. Science. 403. doi:10.1088/1755-1315/403/1/012065
Deochand, N., Costello, M. S., & Deochand, M. E. (2018). Behavioral Research with Planaria. Perspectives on behavior science, 41(2), 447–464. doi.org:10.1007/s40614-018-00176-w
Schmahl G, Benini J. Treatment of fish parasites. 11. Effects of different benzimidazole derivatives (albendazole, mebendazole, fenbendazole) on Glugea anomala, Moniez, 1887 (Microsporidia): ultrastructural aspects and efficacy studies. Parasitol Res. 1998;84(1):41-9. doi: 10.1007/s004360050354.