Aquaponics: the organic hydroponic system

Is it possible to grow in hydroponics using organic nutrients without ending up with clogged drippers or deteriorating the nutrient solution? The answer may lie in aquaponics, a system that combines aquaculture with hydroponics to create a circuit in which fish waste is transformed into nutrients that can be used by plants.

Although it is often presented as a modern technique, the idea of integrating the production of aquatic animals and plants has very ancient roots. There are historical examples of combined fish and plant cultivation systems in Asia and agricultural techniques such as the chinampas in Mesoamerica. However, modern recirculating aquaponics is much more recent and combines knowledge of aquaculture, biological filtration, and hydroponics.

What is aquaponics?

Aquaponics is a cultivation system that unites two disciplines:

• Aquaculture: the farming of fish and other aquatic organisms.
• Hydroponics: the cultivation of plants without soil, using water as a medium to transport nutrients.

In an aquaponic system, fish produce waste rich in nitrogenous compounds. This waste goes through a biological process in which different bacteria transform ammonia into nitrites and subsequently into nitrates. Plants can use these nutrients and, at the same time, help remove certain compounds from the water before it returns to the fish tank.

Therefore, rather than simply speaking of “organic hydroponics,” it is more accurate to define aquaponics as an integrated system of aquaculture and hydroponics based on water recirculation and the activity of beneficial microorganisms.

Is aquaponics a form of organic hydroponics?

The answer depends on what we mean by “organic.”

In conventional hydroponics, nutrients are usually provided through mineral solutions specifically formulated to be soluble and easily available to the roots. This allows for precise control of parameters such as nutrient concentration, pH, and electrical conductivity.

The problem arises when we try to use certain organic fertilizers directly in a hydroponic circuit. Many organic products contain matter that must decompose before releasing its nutrients. That matter can promote microbial proliferation, generate waste, or cause problems in pumps, filters, and irrigation lines.

Aquaponics poses a different solution: the nutrients come mainly from the feed and waste of the fish and are processed by the system’s own bacterial ecosystem.

This does not mean that any organic fertilizer can be added to a fish tank. In fact, introducing products not designed for aquaponics can alter water quality and harm the fish.

How does an aquaponic system work?

A well-designed aquaponic system functions as a relatively closed circuit.

1. Fish generate waste

Fish receive food and, as a consequence of their metabolism, generate waste that ends up in the water.

One of the compounds that requires the most attention is ammonia, as it can be toxic to fish when it reaches certain concentrations.

2. Water passes through a filtration system

Before reaching the plants, the water can pass through a mechanical filter responsible for removing solid particles and larger debris.

This step is especially important to prevent solid waste from accumulating in the pipes or reaching the cultivation system.

3. Nitrifying bacteria transform ammonia

Next, one of the fundamental elements of aquaponics comes into play: the biofilter.

Nitrifying bacteria transform ammonia into nitrites and subsequently into nitrates. Nitrates are one of the main forms of nitrogen that plants can utilize.

Without these bacterial communities, the system would not function correctly.

4. Plants absorb nutrients

The nutrient-rich water finally reaches the hydroponic system.

The plant roots absorb part of the available nutrients and help reduce the load of certain compounds in the water.

Afterward, the water can return to the fish tank and begin the cycle again.

5. Water returns to the tank

A pump is responsible for maintaining water circulation between the different elements of the system.

Therefore, it is not simply a matter of “watering plants with fish water.” For aquaponics to work correctly, you must control filtration, oxygenation, temperature, pH, ammonia, nitrites, and nitrates.

Types of aquaponic systems

There are different configurations for setting up an aquaponic crop. The three most common are floating raft systems, systems with grow beds, and hydroponic systems separated from the tank.

Floating raft system or deep water culture

In this system, plants are placed on floating structures and the roots remain in contact with the water.

It is a simple configuration to visualize and can work well for certain crops, especially leafy greens.

Water oxygenation is fundamental, as the roots remain in permanent contact with it.

System with tank and integrated cultivation

Another possibility consists of placing the tank and the cultivation area very close together, using different stages of filtration and circulation.

The main challenge consists of finding water conditions that are suitable for the fish, bacteria, and plants at the same time.

Aquaponic system with separate tank, filters, and cultivation

A more complete configuration physically separates the different stages of the circuit.

A basic scheme would be:

Fish tank → mechanical filter → biofilter → hydroponic system → reservoir/sump → pump → fish tank

This configuration facilitates maintenance and allows for better control of each part of the system.

In addition, separating the stages allows for the removal of solids before they reach the crop and maintains more suitable conditions for fish, bacteria, and plants.

pH in aquaponics: one of the great challenges

One of the common mistakes is thinking that plants and fish need exactly the same water conditions.

That is not the case.

Plants can utilize certain nutrients more easily in slightly acidic conditions, while nitrifying bacteria function within a different range, and fish also have their own needs.

Therefore, in aquaponics, it is not appropriate to simply speak of a pH of 5.5 for plants and 7.5 for fish as if they were two completely independent systems. In reality, you must seek a compromise range that allows fish, bacteria, and plants to function simultaneously.

As a reference, Oklahoma State University points to a general pH range of 6.5-7.5 for aquaponics and places the compromise interval commonly used in many systems at approximately 6.8 to 7.2.

Temperature and oxygen: two fundamental parameters

The water in an aquaponic system cannot be controlled solely by looking at the pH.

Water temperature

The temperature must be adapted to the fish species and the chosen crop. For example, tilapia is a common species in aquaponics and works with relatively high temperatures, while other species, such as trout, need much colder water.

Therefore, there is no single perfect temperature for all aquaponic systems.

Dissolved oxygen

Oxygen is essential for fish, roots, and nitrifying bacteria.

Oklahoma State University indicates that concentrations above 5 mg/L of dissolved oxygen are suitable for fish, plants, and microorganisms in many aquaponic systems. Furthermore, when water temperature increases, its capacity to hold dissolved oxygen decreases.

Therefore, aeration using air pumps and diffusers can be an essential part of the setup.

What fish can be used in aquaponics?

Not all fish work equally well in an aquaponic system.

Among the species used are:

• Tilapia.

• Trout.
• Catfish.
• Sea bass and other freshwater species.
• Carp.
• Koi.
• Goldfish.

Each species has different needs regarding temperature, feed, oxygen, and space. The choice must be made taking into account both environmental conditions and the system’s objective.

Tilapia is one of the most used species in aquaponic systems, although it is not the only option.

Can organic fertilizers be used in aquaponics?

Here, an important distinction must be made.

The goal of aquaponics is for a good portion of the nutrients necessary for the plants to come from the system itself: fish feed → waste → bacteria → nutrients available for the plants.

Therefore, we should not think about adding organic fertilizer to the fish water in the same way we would in a soil-based crop.

An organic product can contain matter that alters water quality, modifies the microbial balance, or affects the fish.

In some systems, certain supplements may be necessary to compensate for nutrients that do not arrive in sufficient quantities, but they must be selected specifically, taking into account the health of the fish and the water chemistry.

And what about hydroponic fertilizers?

Fertilizers designed for conventional hydroponics are formulated to provide soluble nutrients that are easily available to plants.

For example, at Grow Barato you can find specific products for hydroponic systems such as Hydro Grow A+B by BAC, formulated for hydroponic crops and completely water-soluble.

This is important because a fertilizer suitable for hydroponics does not automatically mean it is suitable for aquaponics. In a system with fish, any product added to the water must also be evaluated for its potential effects on the animals and the biological balance of the biofilter.

Therefore, this type of fertilizer can be a reference for understanding the difference between conventional hydroponic nutrition and aquaponics, but it should not be interpreted as a recommendation to add it directly to the fish tank.

Pest control in aquaponics

This is another point where aquaponics forces a change in how you work.

In a conventional crop, we can resort to different phytosanitary products, but in aquaponics, extreme precautions must be taken because any substance that reaches the water can affect the fish and the microorganisms in the system.

Oklahoma State University recommends prioritizing integrated pest management strategies, including physical and biological methods. It also warns that pesticides can pose a risk to fish.

Recommended control methods

Among the strategies that can be used are:

• Sticky traps to monitor insects.
• Physical barriers.
• Manual removal of pests.
• Biological control using beneficial organisms.
• Hygiene and removal of plant debris.
• Frequent monitoring of leaves and stems.

The basic principle is simple: before introducing any product into an aquaponic system, you must verify that it is compatible with fish, bacteria, and plants.

What about root fungi?

Root problems can appear when water conditions are not suitable.

Instead of trying to solve the problem solely through products, it is essential to first check:

• Water temperature.
• Dissolved oxygen.
• State of the roots.
• Water circulation.
• Accumulation of organic matter.
• Biofilter functioning.
• General water quality.

Prevention is especially important because a root problem can quickly affect the rest of the system.

Therefore, it is not correct to simply state that lowering the water below a specific temperature will solve any fungal disease. The appropriate temperature depends on the fish species and the crop, and reducing it too much could cause problems for the fish themselves.

Advantages of aquaponics

When correctly designed, aquaponics presents several interesting advantages:

Water efficiency

Water is recirculated between the fish system and the cultivation system, reducing the need for constant water inputs compared to certain conventional agricultural systems.

Nutrient efficiency

Waste generated by fish is not considered simply trash, but rather part of the system’s nutrient cycle.

Soil-less cultivation

Plants can develop through different hydroponic systems without the need to use soil.

Integration of animal and plant production

The same system allows for the production of aquatic organisms and plants, provided that both components are correctly balanced.

Disadvantages and difficulties of aquaponics

Not everything is an advantage.

Setting up an aquaponic system requires controlling many parameters simultaneously. An alteration in the fish tank can end up affecting the plants and vice versa.

Among the main difficulties are:

• Controlling ammonia and nitrites.
• Maintaining a stable population of nitrifying bacteria.
• Controlling pH.
• Maintaining sufficient dissolved oxygen.
• Controlling temperature.
• Avoiding solid accumulation.
• Choosing compatible species.
• Avoiding products that could be toxic to fish.
• Maintaining pumps, filters, and pipes in good condition.

In other words, aquaponics does not eliminate the need to control nutrition: it changes the way you manage it.

Is it really possible to do organic hydroponics through aquaponics?

Yes, although it is advisable to use the term with some precision.

Aquaponics allows plants to be grown in a soil-less system where a significant portion of the nutrients comes from a biological process based on fish, their waste, and nitrifying bacteria.

This can reduce dependence on mineral solutions prepared specifically for hydroponics. However, aquaponics and organic hydroponics are not exactly synonymous, and an aquaponic system should not be treated as a conventional hydroponic system to which we have simply added fish.

The key is to maintain a balance between fish + feed + bacteria + filtration + water + plants.

Conclusion: aquaponics, a nutrient circuit based on nature

Aquaponics demonstrates that it is possible to combine aquaculture and hydroponics to create a system in which fish waste is converted, through the action of microorganisms, into nutrients that can be used by plants.

Although the idea of integrating fish and crops has very ancient historical roots, modern aquaponics uses filters, pumps, biofilters, and control systems that make this process much more efficient and predictable.

Therefore, if what we are looking for is a way to grow in water using nutrients of biological origin, aquaponics is one of the most interesting alternatives. Mind you: it is not simply a matter of replacing a mineral fertilizer with an organic one, but of building and maintaining an entire ecosystem in balance.