What to Do If a Fish Dies in the Tank?

Owning a fish tank is an easy way to have some exotic pets. However, what happens when a fish dies? 

Can you leave the dead fish in the tank without any harmful consequences?

Truthfully, you may think fish tanks are easy, but there will be a time you have to put in work to maintain them. 

What are the precise steps you need to take when a fish dies?

Let find out!

What to Do With the Dead Fish in the Tank

The first thing you need to do when noticing a dead fish is removing it from the habitat right away. You cannot leave the dead fish in the tank. 

Fish will start decomposing as soon as they are dead. When the fish rots, it can create bad water that affects the other fish poorly. 

The worst thing that could happen is leaving the dead fish to pollute the water and killing all other fish. This is also what you wish to avoid as a fish owner.

Never Flush a Dead Fish

You should never flush the dead fish. Many people believe flushing a dead fish in the toilet is the best way to dispose of it. 

It may be the most convenient and easy way to dispose of the dead fish, but it is not the best way to go about it. 

The best method of disposing of a dead fish is by burying it. This will ensure the fish is actually dead and won’t wreak havoc in the pipes. It is also a way to provide nutrients to the soil. 

If you don’t want to bury the fish, you can stick it in a plastic bag and keep it in the freezer until trash day. Ensure you throw it out when the trash is due.

Is It Normal for Fish to Die in a New Aquarium?

Typically fish should not die in a new aquarium, especially if you prepared your tank well. If you have a colony of bacteria in the tank, your fish should be fine to swap tanks.

Every tank you have should be ready to house fish and already have a nitrogen cycle. There shouldn’t be any sudden changes.

Using bacteria is the most important thing to keep on hand. Every time you add a new fish, you can add a touch more bacteria to ensure the safety of the other fish in the tank.

What Happens If You Leave the Dead Fish in the Tank?

Decomposing fish will release ammonia. It typically takes a fish 7-10 days to start rotting in the water. This process removes the toxin ammonia, a nitrogenous waste.

Ammonia poisoning is also a prevalent fish disease, and although trace amounts are harmless, a dead fish brings too much. 

The ammonia levels should always be 0 in an aquarium or fish tank. 

You will want to inspect the body to see if it died from any disease. Often, the dead fish will get eaten by other fish in the tank.

5 Steps You Should Do When Your Fish Dies

If you own an aquarium, here are five things you can do to prevent your fish from dying and ensuring the habitat stays healthy.

Remove the Dead Fish Immediately

The first thing you need to do when noticing a dead fish is getting a net or another way to catch it

Don’t use your hands because this method rarely works well, and you never know what the fish died from. It can also waste time. 

If you use your hands or get the water on your hands, use soap and water immediately to wash off any contamination.

You may want to consider wearing rubber gloves. 

Fish nets are easily acquired at your local pet store, and all you need to do is stick it in and swoop up the corpse. Dispose of the body right after catching it. 

If you are unsure of how you will dispose of the body, put it in a bag and then in the freezer.

Test for Ammonia Levels

If you have a fish die from any disease, you will need to start testing your waters. So once you remove the dead fish, you will want to use an ammonia testing kit. 

These kits allow you to stick a strip into the water for 10 seconds and understand what is going on in your tank. Once the 10 seconds are up, you will see the strip change color. 

Match the wet strip color up with the color chart on the box. Then you will have a close estimate of the level of ammonia. 

However, suppose the estimate is not accurate enough for you. In that case, some fish tank owners choose to use liquid water testing kits, which is said to be much more accurate. 

Depending on how big your tank is will determine how fast the decomposing body affects your fish tank. The smaller a tank is, the more likely the entire tank is infected.

If you have a big tank, you may need to test where the fish died and use other strips for more areas.

The results of a safe fish tank should be:

  • 0 ppm of Ammonia
  • 0 ppm of Nitrite
  • Less than 10 to 20 ppm of Nitrate

Though small quantities of ammonia are typically safe, even 0.5 ppm could kill your fish or burn their gills off.

Change the Water

If only a portion of the aquarium is contaminated, you may only need to change that part of the habitat. 

However, if it is a large amount, chances are it will spread quickly throughout the entire tank. 

In that case, you will need to change the entire tank and clean it out, but that is typically not necessary. You should aim to ensure the ammonia is down to 0.25 ppm. 

If you change 50% of the water, it will drop to 50% of the ammonia. Using this rule, you will be able to determine how much of the water needs to be removed. 

If you need to remove that amount, you will want to do it 20% at a time and continue to test the level as you go. 

Large water changes can also cause fish to die, which will create more ammonia to take care of. 

Since you do not need to remove all of the water, you most likely will not have to remove any fish.

Changing the fish around, changing the water, or anything else can stress your fish out.

Use Bacteria Starter

Before you clean the tank and when you first decide to use an aquarium, you should already have a bacteria starter you use. 

Everything produces waste, and the bacteria will help rid your tank of it.

Once you get the ammonia down to 0.25 ppm, the bacteria will take care of the rest. 

However, keep in mind that the bacteria develops really slowly and cannot help clean when a fish dies because the rotting body causes too much ammonia. 

Keep in mind that bacteria is adding another living organism into the fish tank, and they will colonize. There are also several different brands to choose from.

Also read: How to Get Beneficial Bacteria in Fish Aquarium?

Investigate the Fish

If you find the fish and there are no issues with the water, you will want to know what happened. You will want to inspect the fish body, especially if it is not yet rotting. 

There are several things to look for. Here are some common problems outside of polluted water. 

Bite Marks

This indicates you may have other aggressive fish in the tank.

If you do not pinpoint which fish is the aggressor, you may have more dead fish on your hands.

Belly Up

If you start seeing your fish swim funny and then float to the top of the tank, take a breath, and then flip upside down, chances are its thermal shock. 

Even minor temperature changes can lead to death.

Bloated Belly 

This is most commonly known as “dropsy.”

It is not really a disease but is a fluid buildup in the fish. The chances of your fish dying are very high.

Color Discoloration

This is typically a sign of poor water quality, and often discoloration will tell you it was Aeromonas.

Another thing to keep in mind when investigating your fish is that by cleaning the tank too much you can stress your fish out.

Too much stress will cause them to die too.

Final Thoughts

If your fish dies, you need to remove it as soon as you notice it. 

Regardless of what it died from, you will still need to clean out your tank to ensure the safety of the other fish. This will help keep the ammonia down.

The reason to inspect your fish after cleaning the tank or while you’re cleaning the tank is to understand what to change or look for with the next fish. 

It will also help you tell if an entire tank is a risk.

The best way to avoid this is by cleaning your tank regularly and keeping a healthy amount of bacteria to help clean the tank. 

If you keep a well-running habitat, most of your fish should die of old age and not from disease.

Frequently Asked Questions

If this is your first time owning a fish tank, you may have a lot of questions.

Here are most of the answers you need to know about owning a fish tank.

What are the essential items to keep a fish tank clean?

You don’t have to clean your aquarium every day. In fact, that’s the best way to shock your fish (which you don’t want… of course). However, having an air pump will help circulate the water. 

A filter will help clean the debris, bacteria will help lower ammonia levels, and a heater can help minimize temperature shock.

Why is a Nitrogen Cycle important in a fish tank?

When you get a pet, it is your job to protect them, including the fish you buy.

Having a nitrogen cycle already in place helps protect your fish from harmful waste. 

As they live there, they will eat, and they will waste like everything else. Having no way to dispose of that waste can leave your fish at risk.

How do you acclimate fish to a prepared aquarium?

If you are certain that your aquarium has all of the essentials and a nitrogen cycle, you can start adding fish. 

The best way to add fish to your established aquarium is by taking the sealed bag they come in and place it in the aquarium water.

Let it sit for 10 minutes, open the bag and add a small amount of the aquarium water in the bag, then let it sit for an additional 10 minutes.

Repeat this process until the bag is full of water. When it is full, open the bag and let the fish out.

Also read: How Long Does it Take to Acclimate Fish to an Aquarium?

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