What are all of these tiny white worms swimming in my tank?

Posted in Health and Disease

People are quite often horrified when they first notice that their tank is inhabited by 'tiny white worms'. They could be one of three things: Hydra, Nematodes or Planaria. They can esily be identified by the way they move, and where they reside within the tank.


Hydra are small carnivorous animals from the Phylum Cnidaria. They possess a simple cylindrical body with tentacles surrounding its mouth. The majority of Hydra reach sizes between 0.25 to 2.5cm (0.1” - 1”). They are usually tan or brown in colour, and are usually difficult to spot, unless your tank is heavily infested. They are usually confused with worms.

Hydra do not 'swim' per se, however they are capable of floating from one location to another. They will anchor to a spot where there is an ongoing supply of food, or they will just float around in the water. They anchor themselves to their surrounding environment by their 'foot', from where they catch and kill their prey. In the aquarium they can attach to things like gravel, vegetation, stones or filtration equipment.

Hydra prey on small crustaceans, worms, insect larvae or fry. Therefore they are usually associated with tanks raising fry. They are capable of killing fry from 10 to 15mm (0.4”-0.6”). Larger fry that are trapped but manage to escape will most likely die anyway, as an after affect of the Hydras stinging cells. Tanks that feed a lot of live brine shrimp can attract Hydra as well.

Hydra can be introduced into an aquarium by live food, snails, driftwood or water collected from natural waterways. A tank that possesses Hydra is not an unhealthy tank, as Hydra do not survive in poor water quality. However, a well looked after fish tank will not provide enough food to sustain large amount of Hydra.

If your fish tank has a Hydra infestation, there are three products that can be used to remove them. Dactycid, Flubenol and Panacur. To reduce and hopefully eliminate Hydra numbers, water quality should be in top condition, and feeding should be reduced.


There are approximately 10,000 to 10,000,000 species in the Phylum Nematoda. Free-living (ie without a 'host') forms can reach sizes between 1mm to 2 cm (0.04”- 0.8”). Nematodes that live in the aquarium usually reside in the gravel, but when disturbed they swim in a snake like manner. Much like that of a sea snake. They can be easily seen in a bucket after cleaning the gravel.

There are three types of nematodes: parasitic, scavengers and herbivores. The vast majority of nematodes are parasitic. All three are able to live within the aquarium; however the scavengers are usually the most common.

Not all nematodes are a menace in the aquarium, the scavenger nematodes can help break down the organic waste in the aquarium. If you are treating your fish tank for nematodes, make sure you know that they are parasitic, as the medications you use will kill the beneficial worms as well.

Nematodes can be introduced to the aquarium in egg or adult form. Eggs can be present in almost anything that you add to your aquarium; feeders, live plants, driftwood etc. Adult worms are more likely to be introduced by live plants and in the water accompanying your feeder fish.

Populations of nematodes can be reduced or elimated by reduced feedings and increased water changes. There is a product produced by Materpet called CureEx, which kills a range of nematodes.


Planaria are of the Phylum Platyhelminthes. They are not true worms. Some species of Planaria are almost microscopic, and are usually white in colour. One species of flatworm, Dugesia, can reach 1cm (0.4”) in length and are grey in color.

Planaria are free-living animals that are usually found crawling on the inside walls of aquariums at night. They move like a snail or slug along the glass using microscopic cilia for movement.

Planaria are usually introduced to the aquarium by means of feeders, plants or anything else that has come from a tank that has a Planaria population.

Planaria feed on dead and/or rotting flesh, as well as excess fish food left in the substrate. They also eat eggs and newly hatched fry. The numbers of Planaria will increase in a tank that is either overcrowded or where the fish are overfed.

Planaria can be removed from the fish tank by baiting them using meat in a mesh bag. The bag can them be removed from the tank with the Planaria stuck to it. The process should be repeated until the numbers are reduced. The paradise fish will eat Planaria, so if adding these fish to your tank is a feasible option it should be considered. Numbers can also be reduced by regular gravel cleaning and reduced feedings.

References: (lost in conversion of article from phpBB)

- Submitted by Oscar Sheila