Hydra in a shrimp tank: are they dangerous, and how to remove them
Hydra are tiny freshwater relatives of jellyfish and anemones. They often appear in shrimp tanks as small stalks with tentacles stuck to the glass, plants or hardscape. Adult shrimp are usually too large for them, but hydra can catch and eat baby shrimp, so keepers who breed shrimp usually want them gone. Below is how to recognize them, why they show up and the removal methods keepers most often report. This is a summary of hobby references and owner reports, not the result of our own trials.
How to identify hydra
- A thin stalk, usually a few millimeters to about 1.5 cm long, attached at one end to a surface.
- A crown of tentacles at the free end, often four to twelve, that wave in the current.
- Color that's white, tan, brown or green (green hydra carry algae inside them).
- They shrink when touched. Disturbed hydra contract into a small blob and slowly stretch back out.
Hydra mostly stay put, though they can slowly move. If what you see glides like a slug with an arrow-shaped head, it's more likely a flatworm; see planaria in a shrimp tank.
Are hydra dangerous to shrimp?
Hydra catch small prey with stinging cells in their tentacles. Owner reports commonly describe them catching newborn shrimplets, and some keepers report adult shrimp getting stung or stuck briefly, though adults usually pull free. In a display tank with only adult shrimp, a few hydra are often more of a nuisance than a threat. In a breeding tank, a large hydra population is commonly blamed for shrimplets disappearing; see why cherry shrimp aren't breeding for other causes.
Why hydra appear
- Hitchhikers. Hydra and their eggs arrive on plants, moss or in water from other tanks.
- Too much food. Hydra feed on tiny organisms that thrive on leftovers. Overfeeding, and especially live foods such as baby brine shrimp, is commonly linked to booms. See our shrimp food guide.
- A well-lit glass surface near the front of the tank, where food particles collect.
How to get rid of hydra
- Reduce feeding. Hydra populations often shrink when feeding is cut back and leftovers are removed promptly. This also helps prevent them returning.
- Remove what you can by hand. Scrape them off the glass and siphon them out during water changes. Pieces left behind can regrow, so get as much as you can into the siphon hose.
- Use a shrimp-safe treatment. Betel-nut-based treatments such as No Planaria are widely reported to kill hydra as well as planaria and are generally described as shrimp-safe when used as directed. They typically kill snails too. Remove dead material and do a large water change afterward.
- Fenbendazole (last resort). Some keepers use fenbendazole-based dewormers against hydra. It's commonly reported to kill snails as well and isn't made for aquariums, so many keepers try the gentler options first.
Preventing hydra
Rinse or quarantine new plants and moss, avoid pouring water from other tanks into yours (see how to drip acclimate shrimp), and feed only what your shrimp clear within a few hours. Test your water after any treatment so a die-off doesn't cause an ammonia spike; our test kit guide covers what to check.
FAQ
Do hydra kill shrimp?
They are commonly reported to catch and eat newborn shrimplets. Adult shrimp are usually too large, though some keepers report adults being stung briefly.
What causes hydra in a shrimp tank?
Hydra arrive on plants, moss or in water from other tanks, and overfeeding, especially with live foods such as baby brine shrimp, often lets them multiply.
How do I get rid of hydra without hurting shrimp?
Cut back feeding, siphon them out, and if needed use a betel-nut-based treatment that is described as shrimp-safe, following the label exactly. Most treatments also kill snails.
Are hydra the same as planaria?
No. Hydra are stalked polyps with tentacles that mostly stay in one place. Planaria are flatworms with arrow-shaped heads that glide.
Will hydra go away on their own?
Their numbers often drop when food is reduced, but they rarely disappear completely without removal or treatment.
Our take
Hydra are mostly a threat to baby shrimp, not adults. Lighter feeding and siphoning handle most cases, and a shrimp-safe treatment is there for breeding tanks that are overrun, with the trade-off that snails usually don't survive it.
Sources: owner discussions on r/shrimptank and r/Aquariums (2024–2026); manufacturer instructions for betel-nut-based treatments; general freshwater invertebrate references on hydra biology; Google search suggestions for "hydra in shrimp tank" and "how to get rid of hydra." Checked October 2026.