Jellyfish

Bell inversion (eversion)

SignsBell folds inward; the animal cannot swim and sinks to the bottom. Common after sudden changes in salinity or flow, or temperature shock

PreventionMatch salinity and temperature on water changes and change small amounts. Check with a hydrometer weekly. Flow should only gently rotate the bell

Shrinkage (underfeeding)

SignsBell shrinks, oral arms shorten, pulsing weakens, body becomes more transparent. Progresses with underfeeding or poor water quality

PreventionFeed newly hatched brine shrimp 1–2 times daily. Enough that the stomach pouches turn orange

Ammonia poisoning

SignsPulsing stops intermittently; drifting at the surface or bottom; bell margin frays. Caused by uneaten food or inadequate filtration

PreventionAmmonia and nitrite must always be zero. Siphon out leftovers 30 minutes after feeding; change 10–20% of the water weekly

Bleaching (loss of zooxanthellae)

SignsSpotted and upside-down jellyfish lose color, turn white and shrink. Triggered by high temperature, insufficient light or poor water quality

PreventionKeep water at 25–28°C with full-spectrum LED lighting 8–10 hours a day. Do not change lighting abruptly

Melting or chipping of the bell margin

SignsBell edge becomes ragged or turns cloudy white and dissolves. Caused by bacterial growth, poor water quality or abrasion

PreventionSet the flow so the bell does not hit the bottom or intake. Remove biofilm from tank walls frequently

Strobilation

SignsNot a disease, but wall polyps release juvenile jellyfish; overcrowding crashes water quality suddenly

PreventionClean polyps off the walls regularly. Move extra juveniles to a separate container or manage stocking numbers

Holes in the bell from air bubbles

PreventionKeep air stones out of the display tank; put them in the sump. Add water gently without creating bubbles. Bubbles collect under the bell and punch holes

First aidTemporarily stop the flow and gently draw off bubbles under the bell with a pipette. Holes close in a few days with good water quality, so focus on water quality

Intake suction accidents

PreventionCover the intake with fine mesh and keep flow low enough that the bell cannot be sucked onto it. Use a jellyfish-specific tank design

First aidStop the pump at once and pour water over the animal so it releases naturally. Do not pull. Even a torn bell often regenerates if water quality is maintained

Torn or ripped bell

PreventionNever scoop with a net; move with water in a cup or bowl. Keep decorations and heaters out of the display tank

First aidKeep water quality optimal and continue feeding. Even with large losses, recovery is possible if the mouth and stomach remain. Set flow to minimum and let it rest

Loss of oral arms or tentacles

PreventionAvoid mixing species and overcrowding. Remove sharp edges on equipment; leave nothing to rub against

First aidThey regenerate in days to weeks; direct food to where it can reach them. Feed non-eating individuals at the mouth with a pipette

Nematocyst dermatitis (jellyfish sting)

RouteBare-hand contact with tentacles or tank water. Upside-down jellyfish sting through their mucus alone

PreventionWork with gloves; if stung, rinse with saltwater and remove tentacles. Do not rub with fresh water

Vibrio wound infection

RouteTouching saltwater with a wounded hand. Enters through chapped skin or cuts

PreventionWear gloves when you have a wound. Wash with soap after working. See a doctor if redness, swelling and fever develop

Aquarium granuloma

RouteMycobacteria in saltwater enter through skin wounds and form nodules

PreventionWear gloves and wash hands afterward. For nodules that do not heal, see a dermatologist and mention your aquarium

Allergy and asthma

RouteSensitization to brine shrimp eggshell dust or to sting venom

PreventionWear a mask when handling the hatchery. If stung and breathlessness or spreading hives develop, go to the emergency room

Food

• Newly hatched brine shrimp 1–2 times daily, rinsed in saltwater first
• Adults can also take frozen or liquid jellyfish food. The right amount colors the stomach pouches
• Zooxanthellae species cannot live on light alone. Daily feeding is required

Water

• Artificial seawater at specific gravity 1.021–1.024; keep temperature stable for the species
• Change 10–20% weekly. Match the new water's temperature and salinity, then pour gently

Toys & play

• No toys needed. Gently circling in the current is their only exercise
• For upside-down jellyfish, a flat bottom and light are the "playground"
• Lighting is for display. Avoid flickering lights

Nest, bed & hideout

• No hiding place needed. A round tank without corners is the "nest" itself
• Upside-down jellyfish sit inverted on the bottom, so provide sand/mud or a flat floor

Bedding & litter

• No substrate for moon and spotted jellyfish. Sand damages the bell
• Fine sand or a bare tank for upside-down jellyfish
• No decorations, driftwood or live rock

Cage / housing material

Dedicated jellyfish kreisel (round) tank. Clear acrylic or glass with no corners

Size & space

Diameter 3–4 times the bell diameter. At least 15–20 L for three moon jellyfish

Layout

• Cover the intake with mesh; flow just strong enough to rotate the bell gently in the center
• Put aeration and heater in the sump, never in the display tank
• Lighting is needed only for zooxanthellae species. Dim light is enough for moon jellyfish

Placement notes

• Place in a room with stable temperature and no direct sunlight
• Choose a low-vibration spot. Tapping or shaking the tank damages the bell

Exercise, free-roam & walks

• No walks needed. Move them with water in a cup
• Check the flow several times a day and confirm every animal is riding the current
• Pump stops no longer than 30 minutes. Longer stops let them sink and get injured on the bottom

Temperature & humidity

TemperatureMoon jellyfish 15–25°C; spotted and upside-down jellyfish 24–28°C

HumidityHumidity is irrelevant. Evaporation raises salinity, so top up with fresh water

Summer & winter

• Summer: above 28°C they bleach and melt. Use a cooling fan or chiller
• Winter: zooxanthellae species need a heater. Avoid sudden drops for moon jellyfish too

Nail trimming

No nail trimming. Instead, measure salinity, temperature and ammonia at least weekly

Brushing, skin & coat care

No brushing. Instead, scrape biofilm and polyps off the walls to keep the flow clean

Other care

Siphon out leftovers 30 minutes after feeding. Rinse the hatchery and pipettes in fresh water and dry after every use

Protection from predators

• Never house with anemones, fish or shrimp. The jellyfish get eaten
• Position the tank so children and cats cannot put hands or paws in
• Different jellyfish species sting each other, so keep them in separate tanks

Foreign-body ingestion

Jellyfish do not swallow foreign objects as such, but sand or debris that falls into the tank can enter the stomach. If you cannot remove it, do not touch; maintain water quality and wait for it to pass

Being stepped on

A jellyfish dropped on the floor will be crushed if stepped on and cannot recover. Scoop with water in a cup and work over a tray on the floor

Getting pinched

Bells tear when caught in nets, pipettes or intake gaps. Do not use nets; cover intake gaps completely with mesh

Falls

An animal that falls out of a cup disintegrates within minutes on contact with fresh water. If dropped, return it to a saltwater container at once; never rinse under tap water

Escape

No escapes, but they can be flushed out through pump drains. Put mesh on the overflow and check the hose end during water changes

Safe release procedure

1. Take your hand out of the tank immediately and rinse the area with seawater or artificial saltwater
2. Remove attached tentacles with tweezers or the edge of a card
3. Vinegar is often ineffective for the three kept species; treat it as a box-jellyfish remedy. If in doubt, use saltwater
4. After removal, soak in 40–45°C water for 20 minutes to ease the pain

After the release

Go to the emergency room if swelling spreads, breathing is difficult or hives cover the body. See a dermatologist for persistent itching

What to tell the vet & what to bring

Temperature, salinity, ammonia reading, water-change date, feeding details, photos and video of the tank. Consult a vet that treats invertebrates or an aquarium

Checking consciousness, breathing & heartbeat

• Pulsing: a moon jellyfish pulses regularly about 30–60 times per minute
• Posture: normal if bell-up and riding the current
• Stimulus response: it is alive if the bell contracts when lightly hit by a gentle flow

Stopping bleeding

• There is no blood. If stomach contents leak from a tear, siphon them out along with leftovers
• Isolate a torn animal in a separate container of clean saltwater and let it rest
• With optimal water quality a torn bell closes within days

Transport

• Fill a zip bag or wide-mouth container 70% with tank water and seal with no air left
• Keep the temperature with ice packs or hand warmers on the outside; avoid vibration and light