Why Are My Fish Dying In My Aquaponics Set Up?

Several factors may explain the fish kill in your aquaponics garden. A majority of these involve poor water quality, leading to fish stress. When fish are under stress, their health is negatively affected, exposing them to various diseases.

Is it common for fish to die in aquaponics?

Although aquaponics mimics fish' natural habitat in an ecosystem, there will still be some instances wherein fish die inside their tanks. This can be attributed to some elements such as poor water quality, mishandling of the fish, and harmful organisms.

Having a well-maintained aquaponics system is an effective deterrent against fish kill. Since the fish thrive in water, it is essential for you to observe proven practices that help maintain premium water quality.

What are the reasons for fish kill in an aquaponics system?

A fish kill in aquaponics is commonly attributed to many factors. Here are those:

High nitrate level

Long-term exposure to moderate to high levels of Nitrate content in aquarium water causes nitrate poisoning in fish. The fish will begin to show signs of nitrate poisoning if there are 20 or more PPM (parts per million) of Nitrates in the water.

Aquaponics fish are harmed by a sudden increase in nitrates, which can be fatal. Overfeeding or overcrowding in smaller fish tanks causes an uncontrolled build-up of dissolved organic compounds, which causes nitrate poisoning.

Excessive ammonia level

Ammonia poisoning occurs when the ph level in a fish tank rises, disrupting the nitrogen cycle. Ammonia levels should be negligible in optimal water conditions.

Although there are many reasons for ammonia to exist in the system, it is hazardous to both plants and animals at high levels. If not addressed swiftly, too much ammonia in the fish tank could kill fish.

Overfeeding fish is one primary reason for a spike in ammonia levels in your tanks.

Low oxygen levels

If your oxygen level is below what is required, this will cause your fish to try to 'breathe' faster than they should, causing chronic stress and eventual fish death.

Dissolved oxygen levels in the water are varied for different fish. For example, trout require 6ppm dissolved oxygen. Other, more 'hardy' fish, on the other hand, require less.

So what causes the drop in oxygen level?

First, the climate: Warmer water stores less oxygen than cooler water; therefore, oxygen deprivation is more common in the summer.

Second, overstocking of fish: A crowded fish tank leads to fish competing with the limited resources they have, oxygen included.

Overstocking of fish

Overcrowding the tank with fish could lead to disastrous results, including the untimely death of your fish. When you have an overstocked fish tank, the water quality worsens over time, considering that many fish excrements fill the water. Aside from this, there is a significant demand for oxygen, which limits your system's ability to satisfy that need.

One of the most common aquaponics blunders that many new aquaponics farmers make is overstocking their fish tanks. While your fish may be tiny at first and acceptable in terms of numbers, fish grow. As a result, your aquaponics fish will become more demanding on the water supply and use more oxygen, lowering water quality.

Incorrect pH range

If you really think it through, an aquaponics system is a compromise between the appropriate pH range for fish and the ideal pH range for plants. For this very reason, growers should monitor their pH frequently to verify that their system is operating at maximum efficiency.

I believe that a pH of roughly 6.4 to 7 is optimal for keeping both fish and plants happy. Anything outside this range will affect fish's health, making them suffer, which could also lead to their demise.

Water temperature is not in the recommended range

Temperature is vital to fish, and the appropriate water temperature varies depending on the fish and plant species reared in an aquaponic system. When the temperature goes outside of the recommended range, it is typically because of the temperature change in your region. A malfunctioning component, either a heater or a cooling system, can also cause this situation.

If the water temperature is beyond the recommended range, the situations below will occur:

  • Fish will eat more food which leads to increased ammonia and nitrate levels
  • Oxygen's solubility diminishes, resulting in a lesser supply of the gas

On the other hand, if the water temperature is below the approved range, the following will occur:

  • Some fish will not eat, which could lead to malnutrition and death
  • Bacteria will not break down fish wastes, contaminate the water, and contribute to fish death

When the system's temperature is too high or too low, the fish body will be stressed, making them susceptible to diseases.

Fish are fighting

Certain fish species are violent and may attack other fish. This is yet another way for your fish to become agitated and stressed. While mixing different fish species can be beneficial in some situations, there are predatory fish to be cautious of. Certain fish can be territorial and fight your other fish if they feel threatened. Apparently, the well-being of your fish is endangered.

How can I prevent fish kill in my aquaponics system?

Each step below corresponds to the causes of fish kill I mentioned above:

High nitrate level

Control the feeding rate of your fish. Too much nitrate level indicates excessive fish waste in your fish tanks. By minimizing the amount of food your fish receive, you also control the solid excretions they produce.

Excessive ammonia level

This issue can be solved by improving the aeration in your system since it improves the water movement in an aquaponics setup. The necessary adjustment of fish feeding rates and fish density can also significantly alter the high ammonia levels within your system.

Low oxygen levels

In aquaponics, levels of dissolved oxygen can be enhanced by utilizing a suitably sized air pump and strategically placing air stones in the fish tank and the biofilter.

Another solution is attaching a venturi to the water pump and structuring the system to maximize water turbulence. This setup can aid in addressing the decreasing level of dissolved oxygen in your fish tanks.

Overstocking of fish

To solve this challenge, reducing the number of fish in your tanks or enlarging them to accommodate your growing fish population would be practical.

Incorrect pH range

To elevate pH in aquaponics systems organically, a variety of strategies are available for you to adopt:

  • Change the water in your tank if the pH drops below six. This action will aid in replacing acidic water with more neutral water
  • Using an additive is another effective way of dealing with incorrect pH ranges. Crushed limestone is a recommended additive

Water temperature is not in the recommended range

Here is a short list of suggestions that you can use to avoid water temperature issues in your aquaponics system.

  • Set up your aquaponics system correctly. If you decide to do it outdoors, ensure that your system is protected from extreme cold and excessive heat
  • Be careful in selecting the plants and fish you will cultivate. If possible, choose the species that have a similar water temperature range
  • Construct safeguarding mechanisms against temperature fluctuations. To prevent dramatic temperature shifts throughout the year, employ thermal mass such as a concrete slab or even a shade cloth cover atop your aquaponics fish tank to keep significant fluctuations in water temperature regulated

Fish are fighting

To remedy such an issue, try to identify the bully fish and remove them from the rest of the group. It is also advisable that you rear the same species of fish in your tanks. If you plan on stocking different fish species, ensure that they will co-exist well in your system.


Watching your fish die is a sobering experience for any aquaponics grower. Whatever investment you have for these aquatic animals immediately goes down the drain. This post can facilitate you in avoiding such a dire situation. Just use the information you obtained here, and the chance of fish death in your system will be reduced.

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