Digging into Aquaponics: #3 -The Systems
By Sylvia Bernstein
Welcome back to aquaponics! In my last article we dug into fish. This time we’ll explore the styles of aquaponic systems.
What Types of Aquaponic Systems?
Aquaponic system designs have been adapted from the hydroponic world, and will seem familiar to anyone with a hydroponic background. In aquaponics, however, we always need to consider both the optimal system for growing the plants that we want to grow as well as how efficiently the water for the fish will be filtered. What follows are the four most popular aquaponic system design styles currently in use.
- Deep Water Culture (DWC) or “Raft” Systems
In this system style the plants are growing in holes in a foam board floating on water that comes from the fish tank. The plant roots dangle directly into the water, and because of this the solid waste from the fish water needs to be filtered out before that water reaches the raft. The reason for this is if the plant roots get coated with solid waste they will be starved for oxygen, which will impede their growth and possibly cause death.
Pros – Great for growing leafy greens and other fast-growing, water-loving herbs like basil. Because the plants are not entangled in media, these types of systems are easier to harvest from than other system types. And because of the more active filtration you can generally stock the fish tank more densely than in passively filtered systems.
Cons – The extra filtration step requires equipment and expense up front, and continuous maintenance of cleaning the filters. Also, it is difficult to grow larger, fruiting plants such as tomatoes and cucumbers in these systems because of the instability of the raft and the reduced nutrient levels from the filtration.
- Media-based Systems
In this system type the plants are growing in a “media” substrate that can be any inert, non-decomposing material such as gravel, lava rock, or a variety of manufactured grow media for hydroponic use. No exterior filtration of the solid waste is necessary because it is mechanically trapped in the grow bed itself, and is made bioavailable to the plants by naturally occurring microorganisms and supplemented composting red worms.
Pros – Media-based systems are more intuitive to experienced gardeners because the media bed is very similar to an organic soil garden bed. The lack of extra filtration makes them easier to set up and less time consuming to maintain than raft-based systems, and they generate higher, more diverse nutrient environments for the plants. Also, the media substrate is a much more stable base for growing larger plants because the roots now have something to anchor to.
Cons – Because the plant roots become entangled with the grow media this method can be somewhat cumbersome with fast growing plants, such as lettuce, that are harvested all at once.
- Vertical Systems
This describes any aquaponic system that is growing in the vertical space above the fish tank. The fish water is pumped up to the top of the vertical tower, and it drains via gravity, fertilizing the plants on its way. They are terrific for growing compact plants such as lettuce, strawberries, and herbs.
Pros – These systems are a fantastic way to make use of the premium air space above the fish tanks in a greenhouse or basement.
Cons – Because the water needs to be moved so far up against gravity, they will require a much more powerful pump than for either a DWC or media system. They can also be challenging to light in an indoor environment because most grow lights are not designed to work in a vertical position (T5 fluorescent fixtures work best). Finally, they often do not work well with tall vining plants with large root masses like indeterminate tomatoes and cucumbers.
- Hybrid Systems
This is my favorite design because it mixes any combination of the system types listed above to optimize your growing space and create the best conditions for each type of plant you are growing. We always start with a media based system in order to provide mechanical filtration for the fish solid waste, as well as grow larger, fruiting plants. The water exiting from the media beds is now perfect for entering a DWC system, which is ideal for lettuces, braising greens and basil. The water from the DWC can then drain into a sump tank where it can be pumped up to the top of a vertical tower system for your herbs or strawberries. Or the vertical towers can be fed directly from the fish tank itself as long as there is additional filtration.
Pros – Plants are grown in optimized conditions for their type, and grow room or greenhouse space is optimized. Also, if building the system is half the fun for you, this can be an entertaining way to creatively expand your system.
Cons – This is a more complicated system to set up and manage, which can also mean that it is more costly than a simple media-based system.
There is more than one way to skin the aquaponics cat, and no single system style is perfect for all plant types and grow spaces. Knowing a bit about the plants you are trying to grow, and the system types that are available can create an overall system design that is perfect for your aquaponic gardening needs and wants.
President, The Aquaponic Source – Try Aquaponics – TheAquaponicSource.com
Author, “Aquaponic Gardening: A Step by Step Guide to Growing Fish and Vegetables Together” –http://aquaponicgardening.com/
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Twitter – @aquapon