Zebra Danios Keep Dying: 6 Easy Solutions

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I remember how frustrated I was when my zebra danios kept dying. First one, then two, and soon they had basically all died, and I had no idea why. Luckily, as time passed, I learned why they kept dying and what I could do to fix it. As a result, I now have a thriving, beautiful school of zebra danios in my 55-gallon aquarium.

Zebra danios usually keep dying due to inadequate water conditions, including the wrong pH, ammonia, and temperature. That typically induces stress in danios, turning the fish susceptible to predators and diseases. However, danios also tend to die when overfed or if the tank wasn’t properly cycled.

As we proceed, I will go through the quick fixes for these most common problems. If you are in a rush, I will say now that the most crucial step is to check the water parameters. I personally do that by using the API Aquarium Test Kit (link to Amazon).

Why do my Zebra Danios Keep Dying?

Zebra danios are tough creatures that can survive in a variety of environments. It isn’t normal for the fish to die in large numbers. One or two deaths in your zebra danio population isn’t necessarily a cause for concern. 

But if you keep losing zebra danios, you have to investigate the situation because it means that something has gone terribly wrong with your aquarium. You must identify the factors that have made life in the tank unbearable for your fish, factors like the following:

1. Inappropriate Water Changes

Water changes are supposed to protect your fish by keeping their environment clean. However, in some situations, a water change can do more harm than good:

  • Stability – First of all, most fish require stability. Zebra danios are no different. If you have forced them to endure the wrong parameters in an aquarium for a long time, they will grow accustomed to those conditions. 

In that regard, they won’t appreciate massive water changes because they alter the water’s chemistry so drastically that they induce stress and shock in the danios.

  • Toxins – People perform water changes to remove toxins from the water. However, a water change can achieve the opposite result. It can introduce toxins into your tank without your knowledge. It isn’t just chlorine and copper that concerns aquarists. 

Some water sources have large quantities of ammonia that will harm all the zebra danios in your tank, eventually killing them if their conditions are not improved.

2. The Danios Were Overfed

Overfeeding is one of the most common threats that beginners face. This is because some aquarists do not realize that fish will keep eating if you keep feeding them. They are unaware that overfeeding is a danger to fish, causing potentially fatal conditions like constipation, swim bladder disease, fin rot, and swelling, to mention but a few.

Additional consequences of overfeeding that can ruin the health of zebra danios before killing them include:

  • Pollution – Overfeeding pollutes the water. First of all, it compels zebra danios to produce a lot more waste than average. Secondly, it allows leftovers to chock the aquarium. Leftovers and waste eventually decompose, producing ammonia that will poison your fish.
  • Algae – Algae feeds on ammonia and the other nitrogenous elements produced when leftovers and waste decompose.[1] You don’t want the algae population to run amok. Besides competing for resources with your organic plants, the algae can create an oxygen deficiency.
  • Maintenance – Overfeeding makes tanks difficult, if not impossible, to maintain. Not only do toxins accumulate at a faster rate, but leftovers can clog the filter. In the end, toxicity and oxygen deficiencies will become a recurring problem until they kill all your zebra danios.

3. The Tank isn’t Properly Cycled

Some will dismiss the possibility that their danios are dying because their aquarium isn’t properly cycled. So it is worth mentioning that you can revert your tank to an uncycled state by washing your filter media in water with chlorine.

The chlorine kills the bacteria in the filter media that neutralizes ammonia and other harmful components. If you wash your filter media with tap water (most of which contains chlorine), your tank is probably not quite as cycled as you would like to believe.

4. The Wrong Tankmates

You have to apply a lot of caution whenever you go hunting for fish that will share your Zebra danio’s tank. You don’t want large and aggressive fish like Oscars and Arowanas in the same aquarium as the danios.[2]

These larger creatures will either eat your zebra danios, deliver fatal injuries or bully them so incessantly that the stress of these encounters kills them. Injured danios are also exposed to diseases like fin rot and the like.

5. The Danios Carry a Disease

Zebra danios are vulnerable to numerous diseases, including swim bladder disease, Vibrosis, mouth fungus, Iridovirus, and hole-in-the-head, to mention but a few. Aquarists are encouraged to quarantine sick fish because certain parasitic, bacterial, and fungal infections can spread from zebra danio to zebra danio if left unchecked.

You can tell that your danio is sick by watching its behavior. It may display symptoms such as lethargy, listlessness, paleness, or swelling. In some cases, you will see the fish gasp for air at the surface of the water.

6. Poor Water Conditions

The wrong conditions in an aquarium can kill all your fish. That includes the wrong pH, temperature, and hardness. Danios will also respond negatively to dirty tanks with toxic water, not to mention small and overcrowded aquariums that are poorly maintained.

The wrong conditions are a problem because they induce stress. They also weaken the immunity of your zebra danios, making them more susceptible to diseases.

What to do if Your Zebra Danios Keep Dying?

Zebra danios are not immortal. They have a limited lifespan. A zebra danio can grow old and die. However, if you are convinced that old age isn’t the cause of the random and continuous deaths in your aquarium, you can use the following steps to save your surviving zebra danios:

Step 1: Improving the Aquarium Conditions

I highly suggest that you create a conducive environment for your zebra danios. That includes the following:

  • Water Parameters

It would help if you kept testing strips and kits on hand. You can use them to ensure that the parameters are accurate. Danios require a temperature of 65 to 75 degrees F, a pH of 6.5 to 8.0, and a hardness (dH) of 5-25.[3]

Keep these parameters stable. That means using a heater to control the temperature with greater accuracy and ensuring that any changes you make to the pH and hardness are slow and gradual.

To measure ammonia, nitrates, nitrites, and pH, I use the API Aquarium Test Kit (link to Amazon). I love that kit because it is easy to use and lasts for hundreds of measures. It comes with the right test strips and reagents to accurately analyze the parameters that matter:

If you want to maintain a precise temperature in your tank, I recommend the Cobalt Aquatics Neo-Therm Pro Aquarium Heater (link to Amazon), which I also reviewed here. This device maintains a consistent temperature and is incredibly accurate, which is what I like about it.

To check the water hardness, I use the JNW Direct Water Total Hardness Test Strips (link to Amazon). I like these because they are small, easy to use, and accurate. You can perform 150 tests with only one box.

  • Environment

Danios are shoaling fish that should be kept in groups of at least five. You have to give them ample space to swim and explore. That means getting an aquarium that is at least 25 gallons. You can get away with 10 gallons. But if you have the means, 25 gallons is safer. 

They also need a layer of sand or gravel and a fair number of plants and decorations.[4] Plants and decorations provide hiding places that protect zebra danios from larger, more aggressive fish. Even in the absence of predators, hiding places put zebra danios at ease, allowing them to overcome stress and its consequences.

Step 2: Picking the Right Tankmates

Find friendly fish whose size doesn’t differ so drastically from the size of your zebra danios. Some suitable tankmates include ember tetras, platys, cory catfish, and small barbs.[5] Avoid fish with long, flowing fins. The zebra danios will nip at them, sparking conflicts that could injure or kill them in the long run.

Step 3: Improving Filtration & Oxygenation

You need a strong filtration system that includes filter pads, canister filters, biological filters, and an active carbon absorption filter. Some people have gone so far as to include a UV disinfection filter.

I also suggest that you improve the oxygen levels in your tank. I personally do that with the Hygger Aquarium Air Stone Kit (link to Amazon). Simply put it in the middle of the tank, and the device will take care of the rest.

Step 4: Proper Maintenance

It would be best if you kept the tank clean and free of pollutants to prevent diseases, infections, and stress from killing your zebra danios. This typically includes the following:

  • Water Changes – Like all fish, zebra danios require weekly water changes. This will prevent the ammonia levels from climbing to dangerous levels. Massive water changes will induce even more stress, which you don’t want. I personally change 10 to 15 percent weekly.
  • Filter– You have to keep your filtration system clean. Otherwise, it will make your water dirty after a while. Canister filters should be changed every week. Carbon filters can be changed every two weeks. You can clean biological filters every six months.[6] De-chlorinate the water before you use it to clean the biological filter media.[7]
  • Cleaning – If you remove the fish and drain the aquarium, you will notice that the bottom and sides are coated with algae and dirt. You have to scrub the algae and dirt off every surface in the aquarium. Create a schedule that allows you to do this before these contaminants ruin the chemistry of your water.

Step 5: Feed Your Danios Properly

I recommend using an automatic feeder to prevent overfeeding. If you don’t have an automatic feeder and you can’t afford to buy one, try to feed your zebra danios no more than twice a day. Give them quantities they can finish in two minutes or less.[8]

Observe your fish. If they finish their food too quickly during mealtimes, you are underfeeding them. But if you keep finding leftovers, you are giving them too much food.

If you are interested in an automatic feeder, I genuinely recommend the Eheim Automatic Feeding Unit (link to Amazon). I love it because it is easy to use and doesn’t require much space. Its timer is reliable and will prevent you from overfeeding your fish:

Step 6: Dealing With Diseases

If your zebra danios are sick, you cannot treat them until you identify the disease. If only a handful of the creatures are sick, you should quarantine them. But if several fish are sick, you can treat the entire tank.

A vet can point you in the direction of the appropriate commercial drugs to use. Some infections will respond to conventional antibiotics. Others require more potent medication. Some diseases will abate once you take basic maintenance steps, such as water changes.

Others require precise solutions such as an elevation in temperature or the application of salt. But again, you cannot proceed until you identify the disease and its source.

Do Danios Die Easily?

Zebra danios do not die easily. Despite their gentle temperament, danios are strong fish that can survive harsh conditions with parameters that differ from the ideal. However, frequent changes in the water chemistry might stress zebra danios, triggering their immune systems to decline.

The best way to make sure that your zebra danios stay healthy is to maintain stable water chemistry. Otherwise, they will succumb to the diseases and infections that their weakened immunity can’t protect them against.

How Long To Zebra Danios Live?

Zebra danios have a lifespan of 3.5 to 5.5 years. While three years is the average, exceptional care can enable them to reach five years. That can be achieved by keeping the water pH between 6.5 and 8.0 and the temperature between 65 to degrees F. 

Danios will tolerate a pH between 5.5 and 9.0, extremes of temperature between 54 to 90 degrees F, and a water hardness of 0-25 dH. However, keeping them in those conditions will shorten their lifespan significantly.

If you found this article helpful, these may also interest you:


While zebra danios are considered hardy, you should still take the time to learn about their needs and water requirements. You have to ensure that you maintain a proper balance in their tank. 

The key to keeping zebra danios alive is to create an environment that is adapted to them. Maintain this environment, and your zebra danios will reward you with their beautiful colors and long lifespan.


  1. http://petskeepersguide.com/7-reasons-overfeeding-fish-bad/
  2. https://www.aquariumsource.com/aggressive-freshwater-fish/
  3. https://www.aquariadise.com/caresheet-zebra-danio-danio-rerio/
  4. https://www.wikihow.com/Care-for-Zebra-Danios
  5. https://www.buildyouraquarium.com/zebra-danio-tank-mates/
  6. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3916945/
  7. https://fishlab.com/why-your-fish-are-dying/
  8. https://www.aqueon.com/information/care-sheets/danio