This is the first of a series of posts that are going to teach you most of what you need to know about Aquaponics in order to build and maintain your own system. These posts are part of a book we are writing and will eventually be selling on our website, so if you’re curious about the most amazing food growing technology on the planet today, watch for this series of educational posts on Aquaponics and please, become interactive by making comments or asking questions. Given the state of our Union, the motto on our website is becoming more important than ever–“Time To Grow Food”.
What is Aquaponics and why should I care?
Aquaponics is an ancient food growing technology that has been around since the Earth has had water with fish and plants growing together naturally. Aquaponics is nature at work. In nature, the fish eat whatever they find for food, and their waste is broken down by the bacteria in the water creating nutrients for the plants. The plants then absorb these nutrients; and in doing so, they clean the water for the fish.
The word “aquaponics” comes from two separate words. The first word is “aqua”, which, of course, means water; but in this case, the “aqua” is from another compound word “aquaculture” (the raising of fish). The second word is “ponics”, which is latin for work, and comes from its use in “hydroponics” (working at growing plants in water, hydro).
So, aquaponics is raising fish and growing plants by using the nutrient rich water provided by the fish.
The reason one should care about aquaponics is that it is a year round food growing system, which can supply you and your family with fresh veggies and fish regardless of the season. Most fish species take a year or more to grow out to edible size. Because of this long term growth, the system must be placed in an environment that allows for year round operation. In tropical climates, an aquaponics system can work outside with minimum cover. In milder climates, it must be placed in an environmentally controlled green house. In harsh climates, it must be placed indoors with grow lights to replace the sun and grow your plants.
The plants grown in an aquaponic system grow out in less time, grow year round, can be planted more densely, are tastier and require 90% less water than does tillage farming. Also, if the aquaponics system is properly designed, it takes up much less space than does tillage farming. The plants can be grown directly in the fish tank to absorb the nitrates from the water as any one who owns an aquarium knows. Most aquaponics farmers separate their fish tanks from their plant grow beds allowing them more flexibility in the way they grow and in what they grow. The water is circulated between the fish tank and the grow bed using a pump. This is known as a recirculating aquaculture system that contains two food sources, fish and vegetables. Some grow their fish for food while others keep their fish as pets that also serve a useful purpose, which is fertilizing the plants.
But there is a third living organism in the aquaponics equation, the bacteria. They live in what is called a bio-filter. Just like the name says, the biology (bacteria) filters the waste in the water, not by removing it, but by converting it into nitrates. It could be called a bio-converter but it is called a bio-filter instead. In an aquarium, where there are only a few fish for the amount of water, the bacteria live in the water, the sand on the aquarium bottom and on any surface where they can attach themselves. In an aquaponics system, the amount of fish per gallon of water is much higher than what is usually found in an aquarium. This higher density requires an additional amount of filtration; therefore, a separate bio-filter becomes part of the recirculating water path in the system.
Before discussing bio-filtration, I want to address the concern some may have for the high density of fish in the system. In a backyard or home aquaponics system, we are talking about one pound of fish for every three gallons of water maximum at full fish growth. Commercial fish farmers usually run much higher densities, which requires special filtration and oxygenation of the water. Even at three gallons per pound of fish in the system, the fish tend to school together somewhat because it’s the nature of fish to create schools. They were introduced into the same tank when the were very small, grew up together and like to hang out with each other. When fish get stressed, you will know it by their unnatural behavior. At these densities, your fish will appear relaxed and healthy. I will be discussing the fish in much more detail in a later segment.
The fish give off two types of waste, which, if allowed to accumulate, is toxic to them. As with any living organism, fish cannot live in their own accumulated waste. The first type of waste is ammonia, which is secreted from the gills and found in the fish urine. The second type is fish waste solids. We refer to this as fish poo.
The required bio-filter is a part of the aquaponics system. In many systems, the grow beds double as the bio-filer because they have a large amount of surface (substrate) area and function not only as a bed within which to grow the plants but also as a place where most of the bacteria in the system live that convert the ammonia. These bacteria are known as autotrophic bacteria, which attach themselves to any surface they find. Their job is to convert the ammonia into nitrates. This is a two step process. First, one type of autotrophic bacteria convert the ammonia to nitrites by removing the hydrogen from the ammonia and adding oxygen it gets from the dissolved oxygen in the water. For the chemists reading this, it is NH3 or NH4 -> NO2 + H2. The nitrogen (N) is retained and combined with oxygen (O2) forming nitrite (NO2), and the hydrogen (H2) is released. Both are released back into the water.
The nitrites (NO2) produced are also toxic to fish in relatively small quantities, just like the ammonia. So, the second bacteria comes into play to add some more oxygen to the nitrites converting them into nitrate (NO3). Note the spelling, nitrite (NO2), nitrate (NO3). Now, nitrates (NO3) are not very toxic to fish and generally, depending on the species of fish, they can tolerate 100 times more nitrates in the fish water than they can ammonia or nitrites. Remember, plants need and love (absorb) nitrates, so the nitrates won’t stay or accumulate in the water to high levels unless there are fewer plants than needed to absorb (uptake) all the nitrates generated by the fish and bacteria processes in tandem.
This brings us to the solid fish waste. The good news is that nature provides. In this case nature provides us with another type of bacteria known as heterotrophic bacteria. Heterotrophic bacteria live in the water and attach themselves to any dead organic mater like uneaten fish food, dead plant roots or solid fish waste. Through a process called mineralization, the heterotrophic bacteria convert these leftovers into their component parts, which become nutrients for the plants. They also produce their own waste, which is ammonia; and it is converted by the autotrophic bacteria mentioned above into nitrates for the plants. In addition, heterotrophic bacteria keep the water in the fish tank clean and clear. Heterotrophic bacteria also require and consume the dissolved oxygen in the water in order to live and do their work.
It is important to note that the above processes both require and use dissolved oxygen found in the water (as do the fish and plants) and deplete it from the water as they go through their processes. This dissolved oxygen must be replaced on a continuous basis or the process will not work properly. I will discuss the importance of ample dissolved oxygen in your system in a follow up post.
The plants, which are planted in the grow beds, receive the nutrient rich water containing all these wonderful ingredients including dissolved oxygen, uptake them along with some water and use them to grow. The remaining water now has reduced amounts of nutrients, and it is returned to the fish tank for use by the fish. So, the fish are fed, and their waste feeds the bacteria. The bacteria convert their food (fish waste) into bacteria waste that feeds the plants. The plants uptake the nutrient rich food provided by the bacteria. The water is cleaned in the process and returned to the fish. These symbiotic relationships are on-going as this is a recirculating aquaculture system that has both fish and plants as well as natures gift of beneficial bacteria working away, and it is known as Aquaponics.
Part Two will deal with System Design.
L. Oliver Duffy
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