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How to Get Rid of Hydra in Your Aquarium

A miniature tentacle-monster has been spotted in your freshwater aquarium. Not to worry – it’s a fascinating freshwater creature called hydra that is relatively easy to deal with. 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 up to 0.4 inches (1 m) in length and range in color from translucent to green to light brown. 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 have stinging cells that are used to paralyze and catch their prey.

Because of their immortal cells and strong regenerative abilities, scientists have been fascinated by hydra for a long time. When a hydra has been broken into pieces, each part regenerates and becomes a new, unique hydra. They can also reproduce asexually by producing buds or sexually by creating eggs.

Hydra viridissima is the green hydra. It has a special, symbiotic relationship to photosynthetic Chlorella algae. This is what gives it 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, aquatic plants or rocks. You can also introduce hydra if you get wild foods, plants, and hardscape.

Are hydra dangerous to humans? No, the stinging cells are too weak to affect humans. If you try to touch them, they quickly retract their tentacles and ball up to avoid predation from larger animals.

Are hydra bad for aquariums? Hydra are ambush hunters that like to eat microworms, insect larvae, and tiny crustaceans (e.g., cyclops, daphnia, scuds, and baby brine shrimp). 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 big to be eaten, and fry have a strong flight response that causes them to jerk away from any stimulus, like a stinging tentacle.

How to get rid of Hydra

If you don’t have a steady hand, and there is a small amount of hydra to remove manually, it is not recommended. Accidentally breaking off pieces of hydra can cause them to grow into new hydra. Instead, we recommend that you

Reduce the food intake

going into the tank. When hydra don’t get enough food, the majority of them will starve to death 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 method of removal is to allow predators to eat 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 particularly prominent in fry grow-out tanks and shrimp-only aquariums because we purposely overfeed them with hydra-sized foods like baby brine shrimp or powdered fry 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. Plus, snails do a great job of cleaning up any excess food that is not 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. If you are looking to add live plants to your aquarium, it is worth researching to make sure that the chemicals will not harm aquatic animals or plants.