Guide to Aeration in Aquaponics Systems

One of the common mistakes many aquaponics beginners make is not providing oxygen to their system through aeration. Aeration is crucial for the survival of your fish, plants, and bacteria because these elements require the right amount of dissolved oxygen to survive and carry out their functions. This article discusses the importance of aeration, the different types of aeration, and how to install them in your aquaponics system.

What is Aeration in Aquaponics?

• Fish for respiration.
• Plants for respiration, health, the strength of their roots, and nutrient uptake.
• Bacteria for nitrification and respiration.

Dissolved oxygen (DO) is one of the essential parameters for growing fish and plants and is critical to the bacteria that convert fish waste into nutrients for the plants. It is also an indicator of good water quality, which is why aquaponics systems need proper aeration techniques to provide the required dissolved oxygen.

Fish Tank Aeration in Aquaponics

Different fish species need different ranges of dissolved oxygen. Generally, most fish species grow and thrive within a DO range of 4-5 mg/liter. If the DO level drops below 4 mg/liter, fish may swim at the surface, breathe rapidly, and lose appetite. Warm water fish like bluegill, catfish, and bass require about 5 mg/liter of DO, while coldwater fish like trout require about 6.5 mg/liter of DO to maintain good health and growth.

Some fish, like tilapia, are tolerant of lower DO, but it will affect their growth rates. This is one of the crucial factors you should consider in choosing the best fish for your aquaponics system. Oxygen depletion often occurs during summer because warm water holds less oxygen than cool water. High temperatures also increase the metabolic rate of fish, resulting in the need for more oxygen.

Grow Bed Aeration in Aquaponics

Plant roots need oxygen for respiration, a critical plant process that releases energy for root growth and nutrient uptake. During respiration, plants absorb oxygen through stems and leaves, and roots. Most plants need high DO levels, which may exceed >3 mg/liter of dissolved oxygen. Healthy roots with enough oxygen supply can absorb the required nutrients from the water and ensure proper plant growth.

If you have a flood and drain, nutrient film technique (NFT), or dutch bucket aquaponics setup, then you don't need to worry about aeration. This is because plants get natural oxygen from the environment. You have to make sure you are using the right grow media so that your plant roots will have enough air in the grow bed.

However, if you have a raft system, you will need an aeration system in your canals to ensure your plants get the required dissolved oxygen.

How Does Aeration in Aquaponics Work?

Aeration is done by moving water flow or by using air stones. Aeration can be implemented in an aquaponics system in three different ways. These are:

1. Diffused Air Systems

In diffused air systems, the air is diffused in the water by using air stones, which help transfer dissolved oxygen into the water. The size of the air bubbles will depend on how big the pores in the air stones are. The smaller the bubbles, the better the dissolved oxygen flow. However, smaller bubbles require more pressure from the pump. The depth of the air stones also plays a role in the amount of dissolved oxygen created. The deeper the diffuser is, the more water is moved, and bubbles are formed. To learn more about diffused air systems and the use of air stones, click here.

Where to Place the Air Stones in Your System? 

• In a media bed system: Place them in the fish tank because fish need dissolved oxygen.  
• In a raft system or DWC: A raft system needs more oxygen than a media-based system because the roots are permanently submerged in the water. You can also install your air stones in the fish tanks or biofilter. 
• In a Nutrient Film Technique (NFT): Install the air stones in the fish tank or biofilter because an NFT system does not need as much air input as the media-based system.

2. Water Pump-driven Systems

Water pump-driven systems include the use of spray bars, venturi, oxygen saturation cones, and water mixers.

• Spray Bar

This method uses a pipe drilled with small holes to force the water to spray out, allowing degassing and aeration. This work well on water pumps that carry medium to high pressure. This is because smaller fractional hp high-flow pumps do not have enough force to drive the spray bar.

Creating your spray bar is easy. You'll need a pipe with a few holes in it. The main goal is to ensure no stagnant areas in your tank. You can install a vertical or horizontal flow to install your spray bar.

The spray bar is aimed straight across one side of the tank in a vertical flow. It is recommended for smaller tanks with at least 800L and not great for round tanks. Vertical flow leaves the surface water calm, so it is easier to check and inspect the fish tank.

The horizontal flow creates a "Laminar Flow," which means it flows in the same direction everywhere in the tank, relative to the fish. The flow intensity also decreases as it gets deeper, leaving heavier solids undisturbed and giving fish an area to rest. This is great for round tanks and not suitable for long narrow tanks.

• Venturi

• Oxygen Saturation Cone

• Water Mixer

The mixers are designed to create little back pressure so that the water in the system is mixed with water coming through the pipe to increase the flow as much as five times. This method is cheaper and easier to install.

3. Mechanical Aeration

This method uses a driving motor into a spinning blade, prop, or paddle wheel. This method also needs a power source in the water and a submersible motor. Mechanical aeration is usually used in large aquaponics systems.

Conclusion: What is The Best Aeration Method in Aquaponics?

Using an air stone is one of the best and easy ways to promote high oxygen levels because of its portability and efficiency. It is also ideal for backyard aquaponics home growers because it suits well into small systems. An air pump combined with air stones can also serve as an emergency aeration method if  your pump fails, and it is the cheapest way of keeping the dissolved oxygen level of your aquaponics system high.