Dead Fish in the Tank? Guide to Disposing, Cleaning, and More

Dealing with a dead pet fish is an inevitable part of the journey of every fish owner.

You are never ready to lose one and will try your best to save even a suffering fish. Losing a healthy fish is shocking. We are sorry for every fish you lost.

While grieving, you are also worried about – why did it die? Will other fish(es) also die? How to dispose of the dead fish and console your kid(s)?

This article is about the best ways to deal with a dead fish and the immediate actions necessary to save the rest, making it a little easier for you.

Locating a Missing Fish in the Tank

If you notice a fish has disappeared from the tank, you may find your fish lying motionless inside a tank decor, in a corner, or stuck in the filter.

No luck? Search the house. If the jumper fish escaped from the open tank, you might find it (dead or alive).

If it is still missing, maybe an opportunistic tank mate ate it alive. Or the tank mate(s) ate the dead fish, or your furry pet ate the escaping jumper fish.

Consider every possibility carefully and take corrective actions for the future.

How to Know if a Fish is Dead

If you find a fish motionless, do not jump to conclusions. As a fish owner, you must be aware of the behavior trends and sleeping habits of your fish like

• Clown Loaches and Betta Fish play dead for a long time. Clown Loaches sleep on their sides as if dead (refer to the image).

• Bamboo Shrimps remain in the same position for a long time, raising concern.

• If your favorite goldfish/Betta Fish is lying sideways in the bottom or is suspended in the same position in mid-tank, it might not be dead. It might be sick.

• Tap on the aquarium glass. It may move away or respond with slight movements in the same position. If the fish seems unwell, refer to common diseases in aquarium fishes for detailed help.

• If unsure, lift the fish using a net or with your hands (use gloves). It will wriggle and move if it is alive.

• Fishes breathe using their gills. Observe its gill movement. Bettas and Labyrinth fish breathe through their open mouths too. Notice their bellies for breathing movement if there is no gill movement.

• If the fish had escaped outside the tank, check if the scales are intact. If the scales break, the fish will dry and die.

Do Fish Float When They Die

Its corpse sinks to the tank bottom. If unnoticed, there is a chance that an omnivorous tank mate(s) will eat it, and you will never find its dead body.

If uneaten, its internal organs will start decomposing. Gasses that generate in the process make the corpse buoyant. Hence, a dead fish floats after it dies.

How long it takes to decompose depends on factors like the size of the dead fish, tank size, water temperature, etc. When a fish decomposes, it produces high levels of ammonia, which is toxic to other fish(es).

What to do with a Dead Fish

As discussed in section 3.0, a decomposing fish poses an ammonia threat to living fish(es).

Its impact depends on the size of the aquarium vis-a-vis the size of the dead fish.

For example, a small dead fish in a bowl poses a bigger threat. If the same fish dies in a larger tank, the good bacteria might dilute the ammonia levels.

It is essential to remove the dead fish from the aquarium immediately:

• To diagnose the cause of death (infection, wound, etc.) and fix it.
• To detect and stop bacteria/parasites from spreading.
• Eating an infected dead fish or breathing infected water will risk the health/life of other fishes.
• Irrespective of the aquarium size, the view of a decomposing fish (any size) is unpleasant.

If you cannot remove it for an uncontrollable reason(s), follow other remedial measures to save the rest of them.

The following video shows the importance of inspecting a dead fish.

What to When a Fish Dies in the Tank

If the fish was already in a quarantine tank (QT) for treatment, you only need to dispose of it and clean the QT.

Else, follow these steps.

• Use a net to remove it from the tank after confirming it’s dead. Use disposable gloves if removing with your hands. Sterilize the net later on.

• Seal the dead fish in a Ziplock and deep freeze it to stop decaying and smelling. Use an ice cream to pack larger fish.

• Test the tank water parameters on priority to prevent further loss.

• Perform a 10% water change even if all water parameters are acceptable.

• Clean the filter. Change only 50% of the cartridges if need be.

• If you require more than 20% water change to reduce toxic chemicals, add a good probiotic chemical to the water to increase the good bacteria immediately.

• Examine the dead fish to analyze the cause of death.

1. Wounds – could be due to aggressive/fin-nipping tank mates, edgy/rough tank decor, or diseases (like tail rot, fin rot, hole in the head, etc.).
2. Any spots on the body indicate diseases like Ich, Velvet, etc.
3. The presence of copper-based medication, fertilizers, and anti-parasitic medicine in the water can kill certain fishes (like shrimp/loaches, eels, or fishes with no/ small scales, sea stars, etc.).
4. Excessive fertilizer/carbon dioxide injection disturbing the aquarium ecosystem.
5. Got stuck in the filter.
6. Natural death.

• If all/majority of the fish died suddenly, it could be due to the following:

1. Above chemicals.
2. Ammonia or nitrate poisoning.
3. An improper water change or temperature change.
4. Insufficient/no acclimating after purchase.
5. Technical issues (like power failure, fault in the filter system, etc.)

• Take corrective actions according to the cause(s).

• Improve tank management henceforth.

Did you know? In 2017, a Tokyo Aquarium lost 1235 of 1308 fishes due to lack of oxygen.

How to Dispose of a Dead Fish

Flushing it down the drain is a big NO. It may clog the sewage system. Many sewers open directly into rivers. If fish(es) in the wild eat a probably infected fish, they will be at risk.

Your pet fish deserves a dignified closure. You can bury, cremate, or bin it off. Doing this with your kid(s) helps them understand death.

Burying or Potting

A decomposing fish releases rich nutrients for plants to grow.

If you have open space, dig a 4 to 5 inches deep burial pit to prevent stray animals from digging out and eating the dead fish.

Place the fish into a biodegradable box. Bury it. Add a layer of kitty litter to diffuse the smell (optional). Say your prayers. Fill back the pit.

You can leave it as it is, or add a paving slab with/without a note, to identify the burial spot. Planting a tree on the burial site is a great way to complete the cycle.

If you do not have a burial space, you can bury it in a large pot with an outdoor plant in its memory.

Cremating

For safety reasons, do not cremate a dead fish yourself unless you have prior experience.

Your vet/local crematorium can help you with safe cremation.

This process involves drying the fish in an oven. Once the fish cools down, light a fire in a safe spot. Keep the fish in a pot and place it on the fire. Wait for the body to turn into ashes. Disperse the ashes back into nature.

Binning

If burying or cremating is out, seal the fish in a ziplock. Move it to a box and put it in a dustbin.

How to Sterilize a Fish Tank after a Fish Dies

You need not clean the entire tank after a fish dies unless the tank water is infected.

Timely removal of the dead fish from the tank, getting the tank water parameters in place, performing a minimum 10% water change, and taking other corrective measures to avoid future mishaps is enough.

A fish tank will need sterilization if:

1. A fish died from infection (like ich, velvet, etc.) in the main fish tank housing many fishes.
2. The fish was in a quarantine tank (QT) and died. The QT has no fish now.
3. All the fish died.

7.1 Steps to Sterilize an empty Tank (No Fishes)

1. Empty the tank.
2. Prepare a 10% bleach solution using bleach with no chemicals.
3. Sprinkle it liberally on the aquarium walls, decor, and artificial plants. Leave it for 2-3 minutes.
4. Rinse thoroughly to remove bleach traces.
5. Wipe the aquarium walls clean with tissue paper. Keep the aquarium, decor, artificial plants, and substrate in sunlight for 2-3 days.
6. Use a 3% hydrogen peroxide solution to sterilize live plants. Rinse them thoroughly.
7. Fill the tank with dechlorinated water.
8. Add 0.5 ppm household ammonia to catalyze nitrogen cycle.

Follow the appropriate sub-sections hereafter.

7.1.1 Non-infected empty Tank (No Fishes)

1. Add the substrate, decor, and live plants immediately.
2. Clean the old filter and use it with new cartridges or buy a new one.
3. Run the empty aquarium till it matures (normally 6 to 8 weeks).

7.1.2 How to Clean an Empty Tank After a Fish Died from Ich

1. Follow section 7.1.
2. Remove carbon from the filter.
3. Administer an over-the-counter Ich medication.
4. Heat the water up to 90 degrees F for ten days.

7.1.3 Cleaning an Ich-infected Tank Aquarium with Fishes

1. DO NOT follow section 7.1 as it has live fishes.
2. Follow section 7.1.2 (steps 1 and 2).
3. If you have scale less fish, shrimp, or loaches, administer only 50% of the recommended dosage and avoid copper-based medication.
4. Add some aquarium salt (if your freshwater fishes can tolerate it).
5. Change 10% water daily only if you add aquarium salt.
6. Increase the water temperature to 77-82 degrees F for a week.

Add tank setup (for section 7.1.2) and filter carbon and probiotic bacteria (in both cases) after the Ich treatment completes.

For all types of sterilization – Add new fish to the tank only after it matures/treatment completes. Adjust the water temperature according to fishes you wish to add.

Conclusion

After reading this article, you are better equipped to deal with any eventuality.

Life is about learning, accepting, and moving on. So is fish parenting!

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