An Aquaponics Grow Bed is one of the 3 main components in any aquaponics system, the other two being the fish tank and the water transfer system. The grow bed is actually a bio-filter itself in that, the natural bacteria takes up residence on the surfaces of the gravel media. This makes it a self contained ecosystem of bacteria processing ammonia from the fish, and converting it to nitrates that become nutrients for the plants.
Aquaponics Grow Bed Design
Materials to build an Aquaponics grow bed are usually made of plastic, fiberglass, or wood. These containers are then covered with polyethylene sheeting or watertight rubber on the inside walls and bottom.
Be sure you’re are using inert materials to build your grow bed with. This means resources that are Chemically inactive and do not contain toxin’s that can bleed into the water. For example, treated lumber and many metal alloys like iron can corrode and contaminate the system. Always be attentive to the sanitation factor in your aquaponics environment. A balanced microcosm ecosystem is needed for the safety of the fish, the plants, and beneficial bacteria. Unwanted toxins can also disrupt the pH levels required. More about the pH levels recommendations .
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The most popular aquaponics grow media to apply inside Aquaponics Grow Bed is Lightweight Expanded Clay Aggregate (LECA). You can see in this image how it becomes a support for the plants while providing oxygen and creating lots of surface area for the bacteria to collect. These pebbles are also known as Hydroton, lightweight clay pebbles that are hydroponic substrates. Lava rock and porous gravel can be used, just be sure to stay clear of any that contain marble or limestone as these cam affect the pH levels.
Remember, an Aquaponics grow bed is the component that collects fish waist that become nutrients through nitrification- it is bio-filter unto itself.
Grow Bed Container Layouts
Grow beds are a container that provides an area for the plants to grow. In this medium all types of seedlings can grow including vegetables, tropical house plants, orchids, flowers, and even tree start ups.
Please keep in mind that there are literally dozens of variations in aquaponics grow bed layouts. Most growers will start with a simple layout that could be used for a small backyard aquaponic system. The bigger they are, the more complex they can get. They may or may not need accessories like bell siphons, water pumps, and bio-filters etc. You’ll have to decide according to the type and volume of crops you want to grow.
Media Filled Bed
The simplest Aquaponics grow bed is the Media Filled Bed design. As in this image, they are typically filled with media to within 2 inches of the top of a 12 inch deep container. As mentioned before, the best media to use are the Hydroton light clay pebbles.
The pipe on the left is pouring water continuously over the media that is pumped in from the fish tank. The Hydroton media is a self-contained bio-filter because the surface of the clay porous pebbles provide a home for the bacteria to grow. This in turn becomes the rich nutrients that the plants feed on.
Aquaponics Grow beds like the Media Filled Bed design will need to be sturdy enough to hold the weight of gravel media and the water. Holes may need to be drilled on the side of the bed or the fish tank to accommodate pipes that run water in and out of these containers. You’ll need PVC fittings, plastic washers, and silicon caulking to properly waterproof the pipe-to-container connection.
This type of grow bed container also needs to be deep enough to provide the space for plant roots to grow. Typically they will be at least 12 inches deep. This means more media in the bin which leads to more bacteria growth. Since the bacteria converts the ammonia to nitrates that the plants feed on, the result is more fish that can be added to the aquaponic tank.
This type of grow bed may need a water pump that trickles water continuously over the media keeping the roots of the plants moist. Another type of Media Filled Bed used a flood and drain design called the Ebb and Flow system that we go over below.
Ebb and Flow Grow Bed Design (AKA Flood and Drain)
This refers to an Aquaponics Grow bed that is flooded with water from the fish tank, and then drained back to the tank below. This grow bed optimizes the benefits of nutrient-rich water and bacteria that are present. Since this is an ongoing cycle, the gravel media is wetted over and over thus keeping it aerated with oxygen continuously. The same goes for the bacteria living in the roots of the plants, and the oxidation created when the water is returned to the fish tank.
The best way to drain your grow bed is with a Bell Syphon. This device is usually made of a PVC pipe structure that fills the grow bed with water. When the water in the grow bed is full it begins to syphon off the water to a predetermined level. Then it will stop syphoning the water and start refilling the grow bed container again. See image below.
The Floating Raft
Similar to DWC (deep water culture), this Aquaponics Grow Bed is actually a floating raft. They are usually made of Styrofoam ( or polystyrene), and they rest on top of a container of water. Typically plants are placed in cups with meshed bottoms inserted into the Styrofoam flat. The roots grow down into the nutrient rich water below that the fish tank has pumped into through filtration components.
This grow bed is often used by commercial growers because of its higher yield of fish and plants. In this system several large flats, each with its own crop type, are floating on long channels of water. The water has been pumped from a separate fish tank full of ammonia waist excreted from the fish. Along the way a filtration system converts the waist to nitrates and becoming nutrients for the plants to feed on.
NFT (Nutrient Film Technique)
This Aquaponics Grow Bed type is housed in long pipes similar to gutter downspouts you find on buildings. They are usually about 10 feet long and have a narrow channel down the middle where the plants grow.
Some Aquaponics growers use cylindrical PVC pipes 3 to 4 inches in diameter. However, rectangular shaped pipes are recommended because of increase space for the roots on the flat surface bottom. Vinyl fence posts make a good NFT grow bed as opposed to metal pipes that may rust and contaminate the water.
Like the floating raft grow bed, the NFT system implements constant water flow. The plumbing design pumps water from the fish tank and through the channel where the plants grow, and then back to the the fish tank continuously.
The container space is smaller in a NFT Grow Bed therefore a separate bio filter component is needed . This is because the bacteria won’t have enough water and surface area to flourish inside the NFT channels . You can find a bio-filter mechanism online to suit the size of your NFT system. Here is more information about Bio-filters
NFT Grow Beds are used for limited crop types like lettuce and other leafy vegetables. Some smaller veggies that fruit, like strawberries, will also do well.
Aquaponics Tower Grow Bed
An aquaponic tower is a vertical structure that does well with small plants like strawberries. Towers can be made of a vinyl fence post or a 3 inch PVC 10 foot pipe. Small pockets are shaped that support the growing plants instead of a narrow channel. Alternately, you can insert small cups in the openings up and down the length of the tower.
These slats can be cut with a small circular saw or grinder tool. Next, heat the vinyl or PVC making it pliable. This way you can shape the small pocket or insert a small cup. The insert can be made of 2 inch PVC pipe.
Now the structure is filled with porous stone like Clay Pebbles to serve as the media for growing seedlings. In some cases, growers will only put the gravel media in cups with netted bottoms keeping the pipe clear. Overhead irrigation is used to drip water through the tubes. Like the NFT system, water is flowing continuously and a separate bio-filter is necessary.
Some aquaponic growers use towers made of Bamboo. This avoids the use of plastics and vinyl in their systems, although they are rather expensive.