Symptoms to Look For
Check if your shrimp are showing any of these symptoms. Symptoms are grouped by severity to help you assess the situation.
Early Warning
-
Small tentacled organisms attached to glass and surfaces
Visual: Tiny polyps (2-10mm) with thin tentacles extending outward
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Green, white, or brown color with visible tentacles
Visual: Body like a thin stalk, 4-12 tentacles at top
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Hydra contract when disturbed
Visual: Tentacles and body retract into small ball when touched
Moderate
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Shrimplets disappearing despite no fish predators
Visual: Baby shrimp dying or vanishing
Severe
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Multiple hydra visible throughout tank
Visual: Dozens of hydra on glass, plants, decorations
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Hydra population exploding
Visual: Numbers increasing rapidly, covering surfaces
Does this match what you see? If your shrimp are showing multiple severe symptoms, act immediately. Early symptoms give you more time to correct the issue.
Possible Causes
Causes are listed by likelihood. Start with the most common causes and work your way down.
Introduced on Plants or Decor
Hydra commonly hitchhike on aquarium plants, live foods, or decor from infested tanks. They or their eggs are nearly invisible.
Did you recently add new plants, wood, or decorations without quarantine? Hydra often appear 1-3 weeks after new additions.
Introduced with Live Foods
Live foods like brine shrimp, daphnia, or live cultures from outdoor sources can carry hydra or their reproductive cells.
Do you feed live foods? Especially from outdoor sources or cultures? This is a common hydra introduction route.
Overfeeding
Like planaria, hydra populations explode when food is abundant. Overfeeding creates conditions for rapid hydra reproduction.
Is there excess food in your tank? Hydra eat small organisms that thrive on decomposing food. Reducing feeding limits their food source.
Already Present at Low Levels
Small hydra populations may exist unnoticed for months until conditions trigger a population boom.
Hydra may have been present before becoming visible. A change in feeding or organic load triggered visible numbers.
Solutions
Option 1: Chemical Treatment with Fenbendazole
Remove snails before treatment - they cannot survive fenbendazole
- 1
Remove all snails from tank
Fenbendazole is lethal to all snails. Move every snail to a separate container before treatment. They cannot survive the medication.
All snail species will die if left in treated tank
- 2
Calculate dosage
Use 0.1 grams fenbendazole per 10 gallons. No-Planaria is pre-measured. Panacur C (dog dewormer): one 1-gram packet per 100 gallons.
- 3
Dissolve and add medication
Mix powder in cup of tank water until dissolved. Distribute evenly throughout tank. Water may become slightly cloudy.
- 4
Wait 24-72 hours
Hydra die within 24-72 hours. They'll contract, release from surfaces, and disintegrate. May see dead hydra debris in tank.
- 5
Perform water change
After 72 hours, do 25-30% water change. Vacuum substrate to remove dead hydra debris.
- 6
Repeat treatment if needed
If any hydra survive, do second treatment after one week. Usually one treatment is sufficient for hydra (unlike planaria).
- 7
Run carbon and return snails
After 1 week post-treatment, run activated carbon for 24-48 hours to remove residual medication. Then snails can safely return.
Recommended Products
These are informational recommendations only. Not affiliated with any brands.
Option 2: Heat Treatment (Shrimp Must Be Removed)
Requires removing ALL livestock. Not practical for heavily planted tanks or tanks that can't easily have livestock removed.
- 1
Remove all shrimp and snails
Transfer all livestock to a separate container with tank water. Shrimp cannot survive the heat required to kill hydra.
This method requires complete livestock removal
- 2
Raise temperature to 104-106F (40-41C)
Use heater to raise tank temperature. This temperature is lethal to hydra but safe for plants and biological filter.
- 3
Maintain high temperature for 2-4 hours
Keep temperature elevated long enough to kill all hydra and any eggs/buds.
- 4
Allow tank to cool naturally
Turn off heater and let tank cool to room temperature, then back to normal operating temperature.
- 5
Return livestock
Once temperature is stable at normal range, acclimate and return shrimp and snails.
Option 3: Natural Predator Method
Fish that eat hydra may also eat shrimplets. This trades one predator for another.
- 1
Add hydra predators
Certain fish eat hydra: some gouramis, paradise fish, and mollies will consume them. However, these fish may also eat shrimplets.
- 2
Monitor predation
Watch to confirm fish are eating hydra. Some individuals eat hydra readily, others ignore them.
- 3
Remove fish after hydra are gone
Once hydra are eliminated, rehome fish if they're not suitable long-term tank mates for your shrimp.
Prevention Tips
Follow these practices to help prevent this problem from occurring in the future.
- Quarantine all new plants for 2-4 weeks before adding to shrimp tanks
- Avoid live foods from unknown sources - hydra eggs may be present
- Reduce feeding to limit hydra food sources
- Rinse new plants thoroughly and inspect closely
- Consider alum dip for new plants (1-2 tbsp per gallon, 2-3 hours)
- Keep No-Planaria on hand for quick treatment if hydra appear
- Regularly inspect tank for early signs of hydra
- Don't share equipment between tanks without sterilization
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Download FreeHydra are freshwater relatives of jellyfish and corals - tiny predators with stinging tentacles. While fascinating creatures, they're a serious threat to shrimp breeding tanks because they actively prey on shrimplets. Identification: - Size: 2-10mm body, tentacles may extend longer - Shape: Thin stalk body with 4-12 tentacles at one end - Color: Green (have symbiotic algae), white, or brown - Behavior: Attached to surfaces, wave tentacles, contract when touched - Distinguish from: Detritus worms (no tentacles), planaria (flat, gliding), trumpet snails (spiral shell) How hydra hunt: Hydra are ambush predators. They attach to surfaces and wave their tentacles in the water. When small prey (shrimplets, daphnia, small worms) touch the tentacles, nematocysts (stinging cells) fire, paralyzing the prey. The tentacles then contract, pulling prey into the mouth. Why they're dangerous: Adult shrimp are too large for hydra to capture, but shrimplets (1-4mm) are perfect prey size. A tank with hydra may have healthy adults breeding successfully, but no babies survive. This makes hydra particularly frustrating - they prevent colony growth while adults seem fine. Reproduction: Hydra reproduce by budding - growing new individuals from their body. Under good conditions, they can double their population in days. This is why small populations can explode seemingly overnight. Treatment comparison: - Fenbendazole: Reliable, shrimp-safe (remove snails), easy - Heat: Effective but requires removing all livestock - Manual removal: Ineffective - hydra regenerate from fragments - Predators: Variable success, may eat shrimplets too Fenbendazole (No-Planaria, Panacur C) is the preferred treatment because it kills hydra at concentrations safe for shrimp. The same treatment that kills planaria also kills hydra, so both pests can be eliminated with one treatment. Unlike planaria, hydra usually don't require a second treatment - they don't have resistant egg stages. One proper dose typically eliminates all hydra.
Frequently Asked Questions
No, adult shrimp are too large for hydra to capture. Hydra can only catch very small prey - they're dangerous to shrimplets (baby shrimp) but can't harm healthy adults. However, weak or dying shrimp might be scavenged by hydra.
Most commonly from new plants - hydra or their reproductive cells hitchhike on aquatic plants. They also arrive with live foods (brine shrimp, daphnia), in water from other tanks, or on shared equipment. They can exist at low levels for months before becoming visible.
Manual removal is ineffective because hydra regenerate from tiny fragments. If you scrape one off, any remaining pieces can grow into new hydra. Chemical treatment (fenbendazole) or heat treatment are the only reliable eradication methods.
Yes, fenbendazole (No-Planaria, Panacur C) at proper doses is safe for shrimp. It reliably kills hydra (and planaria) without harming shrimp. However, it kills all snails - you must remove snails before treatment.
Hydra are distinctive: small (2-10mm), have a thin stalk body with 4-12 tentacles at one end, attach to surfaces, and contract into a ball when touched. They're not flat like planaria, don't glide like planaria, and have visible tentacles unlike detritus worms.
Usually one treatment is sufficient for hydra, unlike planaria which require two doses. Hydra don't have resistant egg stages. If any hydra survive the first treatment (rare), do a second treatment after one week.
Reducing feeding limits hydra food sources and can slow population growth, but won't eliminate an established population. Hydra can survive long periods without food by shrinking in size. Use chemical treatment for eradication.
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