What Causes Fish To Die Suddenly In An Aquarium?

It’s a lot of fun and incredibly satisfying to manage an aquarium. But the sight of one of your fish drifting lifelessly at the surface of your aquarium can be a frustrating and upsetting sight for aquarists. To prevent this tragedy, it’s first important to understand what causes fish to die suddenly in an aquarium.

Statistically, fish will live longer in a well-maintained aquarium than in the wild, despite what you may have read from the media. Finding your fish dead in just a few hours or days in an aquarium results from particular causes and circumstances that are usually avoidable. So what causes fish to die suddenly in an aquarium? Here are 10 of the most typical reasons and how to prevent it from happening.

What Causes Fish To Die Suddenly In An Aquarium? The 10 Most Common Reasons

The death of any fish, especially when there is no apparent cause, is devastating, and most deaths result from deficits in husbandry and tank management. But no matter what level you are at as a fish keeper, you have the chance to review your tank management and care procedures every time you lose a fish. 

Fortunately, you can prevent most experiences with these ten common causes of fish death in aquariums with the most effective methods to avoid the danger.

1. Overfeeding Your Fish

You may have read it plenty of times already, but you can’t have a list of the leading causes of fish deaths that doesn’t include overfeeding. Overfeeding fish is a common problem, and fish are more likely to die from overfeeding than starvation. This is because not all the food added to the tank is consumed or removed. 

Instead, fish food can sink to the bottom of the tank and remain there, eventually starting to decompose and contaminate the water. (This will also lead to a smelly fish tank!) Fish can also become stressed and more susceptible to various ailments due to the harmful byproducts created when food breaks down.

Fish waste and uneaten food present in the aquarium can cause death for several reasons, including:

  • Low oxygen levels

The decomposition of organic matter (such as fish food and waste) is an aerobic process that uses oxygen and produces carbon dioxide. As a result, the fish in the tank or pond have reduced access to dissolved oxygen.

  • High levels of ammonia and nitrites

Ammonia and nitrites, particularly poisonous to fish, are produced when the protein in fish wastes and uneaten food is broken down.

  • Low pH levels 

Because acids are formed during the decomposition of organic material, it also reduces the pH of the water, just as it does the oxygen level. Each species of fish has a preferred pH range. Therefore, stressed-out fish are those that favor an alkaline pH.

  • Fatty liver

Overeating can cause fatty liver, also known as hepatic lipidosis, which is more frequently found in African cichlids and rainbowfish. It can cause the fish to die by impairing the liver’s ability to operate.

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How To Protect Your Fish And Prevent Overfeeding

Giving your fish no more food than they can consume in less than five minutes is an excellent general rule. You can always underfeed if you’re unsure while experimenting to find the perfect measurements. Keep an eye on the fish at the same time to see if they are all eating or not. If they need another small dose, you may always do so. 

This will become simpler with a proper feeding plan and adequate time intervals. Following a schedule, you can train your fish to get the food at a specific time during the day. Generally, feeding twice a day is advised, although you can choose smaller feeds spaced out more often. Fish prefer to eat in little bites rather than in enormous quantities.

Feeding fish at the right time and in the correct quantity, is essential, as well as feeding them the right food. Poor food will not only leave them malnourished and unwell, but it will also result in additional waste since fish won’t consume it.

Other methods to help prevent the dangers of excess feeding include:

  • With a fine net, scoop up and dispose of any extra fish food after 5 minutes.
  • If you believe you have overfed your fish, use a gravel vacuum or siphon to remove 20 to 25% of the water from the aquarium. While using a siphon, you may remove any food that has sunk to the bottom of the gravel or dirt.
  • Perform a cleaning treatment on your filter system every two to three weeks for any food you may have missed. It is not advised to replace the filter media unless it is older than 4-6 months.

2. Insufficeint Aquarium Space

There are two approaches to selecting an aquarium. The first approach is to choose a tank depending on the available space and then populate it with compatible fish. The second option is to determine the fish you want, investigate their needs, and then purchase the appropriate size tank for their requirements. Regrettably, overstocking a fish tank is what some inexperienced aquarium owners do.

Fish crammed into a tank too small is like a crowded party that starts out lively and enjoyable but quickly becomes uncomfortable. Fish that don’t have enough space to develop, move, and prosper are vulnerable to various issues that can shorten their lifespan.

Problems may include:

  • Reduced life span

It’s not good to believe that a fish can only grow to the size of its tank. One may anticipate that a juvenile fish raised in a tiny tank would have stunted growth, spinal abnormalities, restricted muscle growth, and other developmental health issues. Their lifestyle frequently brings on a fish’s unexpected death and shorter lifespan than expected as stunted, overcrowded fish.

  • Territorial behavior

You need a tank that is big enough for fish to have their own hiding spots and corners so they may if required, get away from unruly tank mates. If not, be prepared to witness aggressive behavior that would not often occur in a tank with ample space. The effects of aggressive behavior might be lethal and generate unneeded stress.

  • Poor water quality from overcrowded fish

If regular partial water changes and gravel vacuuming cannot keep up with the waste bioload, cramming fish into confined spaces can disastrously affect water quality. Overfeeding or introducing too many fish at once will make the issue worse. Fish fatalities are caused by contaminated water.

How To Ensure You Have Sufficient Aquarium Space

The “one-inch-of-fish-per-gallon” guideline is best understood today if you haven’t read or heard about it before. It indicates that you may keep one adult fish in an aquarium with one gallon of water. So, for example, if you bought a 12-gallon tank, you could safely keep six fish, each two inches long.

Another way to ensure adequate space and filtration for the species in your tank is to run your stocking through an aquarium calculator.

3. New Tank Syndrome

Well, now that you have checked your tank size, the next most frequent cause of fish death is unhealthy aquarium water. You’re probably dealing with an aquarium that hasn’t been cycled if your fish keep dying when you move them into a different tank. (Learn how to know when your tank is cycled.)

Ammonia poisoning in the fish is caused by new tank syndrome and can soon turn lethal. Fish frequently pass away unexpectedly and without notice. Due to the high amounts of ammonia and nitrite, the aquarium water is usually hazy and odorous.

Lack of helpful bacteria in the water, which keep the water parameters stable by converting ammonia and nitrite into innocuous nitrogen compounds, causes high ammonia levels in a new tank. If the fish are introduced too soon into a newly bought aquarium, positive bacteria cannot grow, resulting in high ammonia and nitrites that poison the fish.

Since it takes a few weeks for the bacteria to establish themselves sufficiently to keep up with the amount of waste the fish are creating, this often happens in tanks that are just one to twenty days old and sometimes longer.

How To Ensure Your Tank Is Prepared

Constantly testing the conditions of your water is the best method to ensure that the environment is secure for your new aquatic inhabitants. Your new companions are at risk if you welcome them to a tank with high ammonia or nitrite levels. 

Fortunately, when you bring them a sample of the water from your aquarium, most fish and pet stores provide free water testing. Alternatively, you can purchase your own water testing kit online and follow its instructions for home use.

4. Fish Incompatibility

Any fish that an Angelfish can grab in its mouth will be eaten, regardless of how much you wish it wouldn’t. Although it might seem like an extreme example, many fish species cannot coexist with certain other species or even some of their own. 

Every fish species has unique behavioral characteristics. For example, some fish are aggressive by nature and enjoy playing with their tank companions, while other territorial fish will chase after every other fish in their territory. Nevertheless, some fish get along just fine with partners from different species but may struggle with those of a similar sort.

How To Identify Fish Compatibility

When it comes to fish behavior, an expert aquarist might be your finest resource. Spend enough time understanding it to prevent losing your priceless aquatic critters. You can seek advice from owners of pet stores and seasoned aquarists. You can also learn plenty by doing your own research and reading articles about fish.

You can save plenty of time and money by using a decent freshwater fish compatibility chart (PDF) or saltwater fish compatibility chart to determine what will most likely not get along in your tank before you buy a new addition.

5. Poor And Low-Quality Water

Fish require a stable habitat with particular water parameters to survive. These criteria include a suitable pH and salinity level and little to no nitrites and ammonia. Therefore, one of the most vital approaches to prevent your fish from dying too soon is maintaining healthy water for your aquarium’s residents.

Infections, immunological weakness, and a general decline in health are associated with poor water quality. And a variety of factors can cause poor-quality water, but the following are the most common signs of poor-quality water:

  • Cloudy water

Cloudiness is commonly caused by one of three things: overfeeding, new tank syndrome, or overstocking or overcrowding your fish. As mentioned before, all three of these factors are significant causes behind fish suddenly dying.

  • The horrible smell of ammonia from the water

An unpleasant odor indicates excess waste and is commonly associated with extra fish food (overfeeding). The initial step in dealing with this issue would be to replace at least half of your water and reduce your feeding intervals.

  • Green water

You have excess algae in your aquarium if the water has turned green. Rapid algae growth often forms due to excessive sunlight exposure, overfeeding, and high phosphate levels in your water supply.

How To Remedy Poor Quality Water In Your Aquarium

In an aquarium, equipment that filters the water takes the role of natural filtration. Maintaining a balanced and healthy aquarium with a larger tank is simpler. It’s crucial to test the water to ensure nitrite and ammonia have not risen to dangerous levels.

A weekly water change of 15 and 20 percent of the total volume of water would fix many possible issues with water quality. Fresh, mineral-rich water will be added to the tank during the water changes. Adding fresh water every week can replenish the trace minerals in the water consumed by fish, plants, and bacteria.

6. Disease And Parasites

Numerous fish conceal parasites and illnesses within their bodies. And stress from capture and shipment can result in an epidemic in your tank soon after they are placed there, even if it may not be noticeable when you first acquire them. Fortunately, most fish illnesses can be cured if they are discovered early and treated with the proper medication.

Fish are also infected with parasites when they eat intermediate hosts. In addition to fish-eating animals like seals and dolphins, fish roundworms are also carried by bird species such as cormorants and seagulls. They excrete eggs, which produce larvae that live in the water and are often found in captured fish that are taken to pet stores. It is not unusual for fish to have parasites due to this natural process.

The Best Way To Treat Fish Diseases And Parasites

Quarantine tanks are strongly recommended before adding new fish to your main tank. Some fish can cope with parasites, which aren’t the cause of death in most fish. However, the fish’s gills create mucus due to the parasite digging into them, typically leading to asphyxia, which is the actual cause of death. 

Even when the parasites themselves are eliminated, the sores they leave behind frequently grow infected and end in death. Fortunately, each ailment has its own set of therapeutic options. And as you come to know them, you’ll be able to cure them more quickly without causing undue stress to your fish.

7. Improper Tank Management And Maintenance

Unconsumed food decomposes, fish create waste, and potentially dangerous byproducts accumulate over time. The only way an aquarium will remain clean is if you make an effort to do regular maintenance. If not, the fish’s environment would eventually become unhealthy. Due to the lack of management and maintenance, the cause of death could result from various factors.

One of the pastimes that require relatively little upkeep and work is maintaining an aquarium. But maintaining and managing your aquarium is among the first steps any new aquarist must take. Keeping clean, fresh water in your aquarium is crucial for fish, coral, and other invertebrates’ well-being and creating a stunning habitat.

The Basics Of Maintaining Your Aquarium

For novice aquarium owners, not understanding what maintenance to execute when might be a barrier. While experts may argue on some details of aquarium management, everyone may agree that routine maintenance is preferable to none. The following are some frequent, daily, and monthly essential basics.

  • It would be preferable to regularly clean colony-rich regions like the substrate and filter, which should be spaced apart. Remember that excessive disturbance also might disrupt the nitrogen cycle and cause ammonia nitrite levels to rise.
  • Ensure the filter operates at total capacity daily – especially every time you feed the fish. With feeding in mind, gather any excess fish food that hasn’t been consumed in the past five minutes. While at it, ensure the water is at the right temperature.
  • Perform partial water changes weekly or bi-weekly, requiring you to remove 20-25% of water with a water siphon or gravel vacuum. While at it, it would be best to siphon the surface/gravel, remove any waste and unwanted debris, and clean any salt creep and algae off the aquarium glass.
  • A monthly water test should be done to make sure nothing nefarious is developing. Then, when emptying the tank, save a bucket of water for filter maintenance. 

Next, rinse the mechanical filter media with the water saved from the water change. Replace the filter material if it’s seriously blocked or unclean. Avoid changing all of the filter media at once. Instead, save some media to prevent losing too many helpful bacteria.

8. Soap Is Deadly To Fish

All aquatic species can get poisoned by detergents, including biodegradable detergents, if they are present in large enough concentrations.

Fish gills can suffer serious harm from detergents. By damaging their cell membranes and removing the waxes that coat them, soap and detergents can impact the creatures that fish feed, such as insects, leading to dehydration and eventual death. When detergent concentrations reach 15 ppm (parts per million), most fish will pass away.

Detergent can kill fish eggs at concentrations as low as five ppm. As a result, surfactant detergents may reduce aquatic species’ reproduction capacity. In addition, detergents’ phosphates can cause freshwater algal blooms, which emit toxins and reduce the amount of oxygen in tanks. So keep soap far away from your fish tank.

What Soaps To Use And What To Avoid

All soaps that are not aquarium-safe should be avoided. Standard lime cleansers are much more dangerous than regular glass cleaners since they both include ammonia, which is poisonous to fish. Therefore, using vinegar or aquarium-safe labeled cleansers is advised to wipe the surfaces and decorations off with a clean, moist towel afterward.

Hot water may also be used to clean the aquarium equipment. You may also add non-iodized salt to the water you use to clean the tank. If algae or calcium clusters are stuck to the glass, and you can’t get them off with water alone, you might have to scrape them off with a clean razor blade.

9. Cold Temperatures Are Lethal

Fish lack the ability to regulate their internal body temperature since they are cold-blooded, in contrast to warm-blooded mammals like humans and other animals. So if the aquarium’s new water is too frigid, the fish will experience cold shock, lose color, and eventually pass away. Sudden temperature drops in winter may be devastating to fish tanks, especially in colder climates.

Antifreeze proteins are an adaptation that fish that live in cold areas have developed to prevent them from freezing. However, cold temperatures can be fatal to tropical fish. These fish can become lethargic and sluggish at cooler temperatures, resulting in a slow, painless death.

How To Keep Fish Warm During Cold Winters

Smaller tanks like Nano tanks are the best choice if this is your first time experimenting with an aquarium setup without a heater. They put fish under little to no stress since they warm up quickly and keep a constant temperature. 

Increasing the temperature inside your home during the winter months is recommended if you have indoor heating. If you decide not to use a heater, aim to keep your room at just over 76 degrees Fahrenheit. Moving your tank closer to a heat source is recommended if you don’t have a fish tank heater.

10. Fish Experiencing Constant Stress Results In Death

Fish eventually die as a result of stress. It’s only a matter of time. It might take days or weeks, but one thing is sure, if constant stress is involved, your fish’s days are suddenly numbered. Unfortunately, stress makes it difficult for a novice to figure out why an otherwise healthy fish dies. 

Over the past few decades, our knowledge of fish stress has significantly developed, particularly concerning the physiological mechanisms and reactions that affect growth and immune system activity, metabolism, expected behavior, and reproduction ability.

As you will see, nearly everything else in this article produces stress for your fish in some manner. Nevertheless, it is the most prevalent cause of mortality in aquarium fish, and stress management is essential to keeping your fish healthy. 

While it is often hard to tell, some signs that your fish are stressed include:

  • Sliding against the glass and gasping at the surface

A fish gasping at the surface shows signs of stress brought on by unfavorable water quality, typically an absence of oxygen. Sliding over the glass might indicate poor water quality, but it could also suggest that the fish are attempting to leave a crowded or inhospitable region of the aquarium.

  • Illness or disease

The stress may cause fish illnesses like ich, defined by white spots on a fish’s body, and other diseases. You should see the veterinarian about possible remedies if you notice any outwardly apparent conditions or blemishes on your fish.

  • Loss of appetite

A stressed fish will frequently refuse to eat. Compared to when it was first introduced, you may notice a loss of weight or size.

Stress Reduction For Fish

While stress management covers a broad range of possible causes and solutions, the most common and typical triggers and stressors and how to prevent them are addressed throughout this article. You will, however, encounter situations over which you have no control. A fish subjected to far too much stress during transportation before being in your possession is one example among many.

Nevertheless, if your fish is stressed, you must treat him immediately. Stress, if untreated, can result in deadly conditions, including Dropsy and Fin Rot. First, try to detect the source of your fish’s stress and remove it. 

You may achieve this by analyzing your fish’s behavior and checking the water. If your fish’s condition doesn’t improve after doing this, you should discuss your options with your veterinarian.

Closing Thoughts

The first step, as always, to preventing your fish from dying is doing a little research before you even set up your aquarium. What causes fish to die suddenly in an aquarium is most often the result of overfeeding, or issues pertaining to poor tank management. Refer to this guide to help prevent these 10 common issues and we’re sure your fish will thrive for a very long time.

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