Fish Dying in New Tank: 8 Possible Reasons

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For any first-time fishkeeper, watching your pet fish grow and thrive can be very exciting.

Still, taking care of a pet fish isn’t always that easy.

Sometimes, you’ll come across many unexpected factors contributing to fish dying in new tanks.

This can be distressing and saddening, especially when you’re just beginning to take care of pet fish.

Not to worry, though. Today, we’ll dissect eight of the most likely factors that can contribute to your fish dying in its new home.

Fish Dying in New Tank: Causes and Fixes

If your fish dies in a new tank, seemingly without any initial problems, there are many possible reasons you can look at.

Here are some of the most common:

1. New Tank Syndrome

Fish naturally produce ammonia and nitrates as waste products, which they then release later into the water they live in.

When fish have uneaten fish food, these may also end up decaying inside the fish tank, significantly increasing ammonia levels.

These factors altogether can lead to early fish death, especially in a new tank.

New tanks still haven’t developed the right chemistry to support fish life.

Because the tank still hasn’t established the capacity to balance out contaminants, fish may die due to the fatal levels of ammonia and nitrates.

This phenomenon is what is known as New Tank Syndrome.

What You Can Do:

First, make it a habit to check your tank’s nitrate and ammonium levels.

If they’re getting higher, you may want to change the water to reduce them to levels that are safe for your fish.

Additionally, consider doing a fishless cycle when you first buy a tank.

Doing this can prepare it to be a safe environment for your fish.

2. Changes in Water Chemistry

A balance in water chemistry is essential for fish to thrive and be healthy.

However, it’s very easy to disrupt this delicate balance.

Suddenly changing large quantities of water may disturb the careful balance in water chemistry.

The result? The change can shock the fish and lead to its death.

What You Can Do

When changing water, simply swap small quantities at a time.

Then, you will want to wait around two to three days before replacing more water.

Doing this will allow the fish to acclimate to the initial changes.

3. Poor Water Quality

The fish tank is your fish’s home, so it’s no surprise that its health can directly be affected by poor water quality.

For instance, high levels of nitrates and ammonia can be fatal to your fish.

Other factors, like putting freshwater fish in a saline environment, also contribute to poor water quality.

What You Can Do

Before deciding to care for a pet fish inside your tank, check the kind of water that they need.

Research the water salinity, pH levels, and other necessary information you need about the environment they will most likely thrive in.

why is my fish dying in new tank

4. Fluctuations in Temperature

Some fish can tolerate fluctuations in water temperature in the tank, but others cannot.

Moreover, a drastic temperature change can also shock fish, depriving them of enough time to adapt to their environment.

This may cause significant stress, which will then directly impact their health.

What You Can Do

Put your fish tank in a suitable location where they are away from possible factors that can cause sudden temperature changes.

Position your aquarium away from direct sunlight, as well as cooling and heating vents.

Additionally, you may want to regularly check your tank heater to make sure it’s functioning correctly.

5. Presence of Toxins and Contaminants

Even the littlest amounts of toxic contaminants can be detrimental to your fish’s health.

When sprays, insecticides, or soap get into the water, it can be fatal and lead to your fish’s death.

What You Can Do

The best thing to do is to get a good cover to protect your tank from contaminants.

Additionally, it’s good practice to use a dedicated bucket for changing water to prevent other contaminants in the bucket from mixing with the water.

6. Overfeeding

Feeding your fish multiple times a day can upset the delicate chemistry of the water in the tank.

Uneaten food can also decay in the tank, releasing high levels of ammonia into the water.

This can ultimately be fatal to your fish’s health.

What You Can Do

Try to create a feeding schedule for your fish, and follow it to a tee.

Be specific about the amount of food you give the fish during their feeding schedule, and don’t give them more than what’s enough.

7. Stress

Just as with humans, stress can also cause health complications with fish.

Fish can get stressed due to constant disturbances, loud noises, and even bullying from other fish.

What You Can Do

Place the fish tank in an area of the house that isn’t too busy.

This way, the fish won’t constantly be disturbed by people coming and going.

Additionally, it’s a good practice to check fish compatibility if you’re looking to have different fish species in your aquarium.

8. Overcrowding

Don’t get carried away when purchasing fish.

After all, overcrowding is a common cause of fish dying in a new tank.

Your aquarium may be too small for your fish, or there may simply be too many of them in a single tank.

This can deplete oxygen in the water, leading to their deaths.

An overcrowded tank can quickly increase ammonia levels in the water, causing health concerns and even death.

What You Can Do

It’s essential to consider your current fish’s growth before buying more fish.

If not, your tank may prove too small to accommodate all of them.

Alternatively, you may opt to buy a bigger fish tank if you’re ready to take care of more fish.


Multiple factors contribute to fish dying in a new tank way too early.

Fortunately, you can easily resolve this as long as you’re aware of what to watch out for.

If you’re a new fishkeeper, remember the possible causes outlined here, and take sufficient precautions to avoid them.

That way, you can take care of your fish without any worries.

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