Planaria are small flatworms that show up in freshwater aquariums, and they’re a genuine threat to shrimp, snails, and fish fry. Getting rid of them requires either chemical treatment, physical trapping, or a combination of both. The key challenge is that planaria eggs can take up to 48 days to hatch, so a single dose of anything rarely solves the problem for good.
Make Sure They’re Actually Planaria
Before you treat your tank, confirm what you’re dealing with. Planaria have a distinct arrow-shaped or triangular head with two visible eyespots that look like tiny crossed eyes. If the worm you’re seeing has a round head, no visible eyespots, and you can see its internal organs through a translucent body, you’re likely looking at rhabdocoela, a harmless flatworm that doesn’t need treatment.
Planaria glide smoothly along surfaces and are usually white, brown, or gray. They’re most active at night and tend to congregate near food sources. If you only see one or two, there are almost certainly more hiding in the substrate and filter media.
Why Planaria Appear in the First Place
Planaria explosions are almost always tied to excess organic waste. Overfeeding is the most common trigger. Uneaten food, decaying plant matter, and a dirty substrate create the conditions planaria need to reproduce rapidly. They can hitchhike into your tank on new plants, driftwood, or even in bags of new shrimp or snails.
Reducing feeding is an important first step regardless of which removal method you choose. If you’re feeding your shrimp or fish daily, try cutting back to every other day and removing uneaten food within two hours. Vacuum your substrate thoroughly. These steps won’t eliminate an established population, but they’ll slow reproduction and make chemical or physical treatments more effective.
Chemical Treatments That Work
Fenbendazole
Fenbendazole (sold as Panacur C or Safe-Guard for dogs) is the fastest-acting option. The effective dose is roughly 0.1 grams per 10 gallons, or about 1 gram for a 100-gallon tank. In side-by-side comparisons, fenbendazole killed visible planaria within hours. One hobbyist documented a planarian on the glass freezing and dying almost immediately after dosing, and by day three, no living planaria could be found in the treated tank.
After dosing, do a 50% water change the following morning. You’ll likely see dead planaria on the substrate about two days later, turned an off-white color. Do another 50% water change at that point. Fenbendazole is safe for shrimp at these concentrations, including sensitive species. It will, however, kill snails. If you keep nerite, mystery, or other snails, remove them before treatment.
No-Planaria (Betel Nut Extract)
No-Planaria is a commercial product made from betel nut extract. It works more slowly than fenbendazole but is widely available and specifically formulated for aquarium use. It targets planaria selectively, though it can also harm snails. Follow the package directions for dosing based on your tank volume.
The Critical Rule: Repeat Treatments
This is where most people fail. Planaria eggs are resistant to all chemical treatments, and those eggs can take up to 48 days to hatch. A single treatment kills the adults but leaves eggs untouched. For complete eradication, treat your tank seven times, spaced one week apart. That schedule ensures you’re catching newly hatched planaria before they can lay eggs of their own. Skipping treatments or stopping early because the worms seem gone is the most common reason for reinfestations.
Trapping as a Supplement
Planaria traps won’t eliminate an infestation on their own, but they’re useful for reducing the population before chemical treatment or for monitoring whether your treatment is working. You can buy commercial planaria traps or make one from a small container with holes poked in the sides.
The best bait is raw meat. Raw pig liver and raw chicken both work well. Some hobbyists skewer the bait on a toothpick to keep it elevated above the holes so planaria have to enter the trap to reach it. Place the trap in the tank at night and check it two to four hours later. Leaving it longer risks the bait fouling your water. You can repeat trapping nightly to pull out large numbers before starting chemical treatment.
Protecting Your Other Tank Inhabitants
Both fenbendazole and betel nut extract are safe for shrimp at proper doses, but they pose a serious risk to snails. Any snail species you want to keep alive needs to be relocated to a separate container before treatment begins and kept out for the full duration of your treatment cycle (at least seven weeks if you’re following the recommended schedule).
Dead planaria release organic waste as they decompose, which can cause ammonia spikes in smaller tanks. The 50% water changes after treatment are not optional. In tanks under 20 gallons, monitor your water parameters closely during the first few days after each dose. Running activated carbon in your filter 48 hours after each treatment helps pull residual medication and organic waste from the water.
Preventing Them From Coming Back
Once you’ve completed a full treatment cycle, prevention comes down to controlling organic waste. Feed only what your tank inhabitants can consume in a short window, and remove leftovers promptly. Vacuum your substrate during regular water changes, paying attention to corners and areas under hardscape where detritus accumulates.
Quarantine new plants and decorations before adding them to your tank. A prophylactic dip or soak with fenbendazole or No-Planaria can kill any hitchhiking planaria or eggs on new plants. Some experienced shrimp keepers treat every new addition to their tanks as a matter of routine, which is the most reliable way to prevent reintroduction. If you’ve fought planaria once, that extra step is worth the effort.