How to Get Rid of Hydra in Your Aquarium

A miniature tentacle-monster has been spotted in your freshwater aquarium. You don’t have to worry about it – it’s a beautiful freshwater creature called hydra and is very easy to handle. Keep reading as we talk about what is hydra and a few natural methods of removing them without harming your animals, plants, or beneficial bacteria.

What is Hydra?

These tiny, freshwater organisms of the genus Hydra are the distant relatives of jellyfish, corals, and sea anemones. They can grow to as large as 0.4 inches (1cm). Their colors range from translucent white to light brown, and green to yellow. Similar to a sea anemone’s hydra, it has a stalk, or foot, that attaches on surfaces (like glass, plants, hardscape, and glass), and a mouth at one end that is surrounded in long, wispy, tentacles. These tentacles contain stinging cells, which are used to paralyze prey and catch them.

Scientists have long been interested in hydra because of their “immortal” cells and powerful regenerative abilities. Each fragment of a hydra can be regenerated to create a new individual hydra by being broken down. They can also reproduce asexually by producing buds or sexually by creating eggs.

Green hydra (Hydra viridissima) has a unique, symbiotic relationship with photosynthetic Chlorella algae, which is responsible for its green pigment.

How did hydra get in my fish tank? In our experience, we’ve noticed that hydra often lays dormant in fish tanks for many months, but then the population blooms when you start heavily feeding baby brine shrimp. You can also suspect that the hydra may have gotten into your fish tank from decorations, rocks, driftwood, or aquatic plants that were infected. You can also introduce hydra if you get wild foods, plants, and hardscape.

Is hydra harmful to humans? The stinging cells of hydra are too weak to cause any harm to humans. If you try touching them, they will quickly retract your tentacles to protect themselves from predation by larger animals.

Are hydra harmful to aquariums? Hydroplanes are predators that eat microworms and larvae as well as tiny crustaceans like scuds and scuds. In our experience, they are a natural part of the aquarium ecosystem and do not seem to greatly impact baby fish and shrimp populations. Adults are too large to eat, and fry have strong flight responses that cause them to run away from any stimulus like a stinging tendacle.

How to get rid of Hydra

Manual removal is not recommended unless you are able to hold a steady hand with a small number of hydra. Accidentally breaking off any hydra will cause them to grow into new hydra. We recommend that you first

Reduce the food intake

going into the tank. If hydra aren’t fed enough, they will die from starvation and eventually disappear. Consider target feeding the fish or using feeding dishes for shrimp to prevent the food from spreading throughout the aquarium. Regular water changes and gravel vacuuming will reduce the number of fish to an almost unnoticeable level.

Another natural removal method is to add predators to eat the hydra. You can try just about any omnivorous or carnivorous fish that is small enough to notice the hydra – such as guppies, mollies, betta fish, paradise fish, and gouramis. If the fish do not seem to consume the hydra, try reducing feedings to whet their appetites.

Aquariums with adult fish and snails rarely get large hydra populations because hydra is a convenient source of live food.

Hydra are especially common in shrimp-only and fry-only aquariums. This is because they are fed hydra-sized food like baby brine shrimps or powdered fried food. Additionally, any potential predators larger than a hydra can be removed. Luckily, you can add snails (like ramshorn, pond, and spixi snails) that are happy to consume hydra but are too slow to go after baby fish and shrimp. The snails are also great at cleaning up any food that has not been eaten by the fry.

People often prefer to use chemical treatments (such as deworming agents or planaria remedies) to kill hydra, but many of these methods are not safe for snails, shrimp, fish, plants, and/or beneficial bacteria. You can also consider treating live plants and decor before adding them to your aquarium, but do your research to make sure they will not adversely affect the plants and aquatic animals.

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