What is Aquaponics? A Primer for Newcomers

Aquaponics is a food production system based upon mother-nature’s own method of recycling fish waste by feeding it to plants.  In a nutshell, that’s the bare-bones definition. It is highly adaptable to home-based use, is low maintenance, produces very high amount of food/area (food density), and requires very little external inputs.

This article is going to focus on the basic concepts and where you can go for further research. It is difficult to explain everything there is to know on the subject because this is a system you need to learn for yourself in order to adapt and apply it to your own locale. Hopefully the following information will help you decide if AP is for you, and if so, how to get started
How it Works – Layman’s Version

Live fish are grown in a tank. Tank water, which contains fish waste, is pumped from the tank to grow-beds. Grow beds are simple containers filled with gravel and which have plants planted in them on top. Gravel in the grow beds will naturally come to host bacterial colonies which will convert fish waste into plant food. Plants consume the food, water is returned to the fish tank via gravity, and you get to eat organically grown fruits, vegetables, and fish. The fish are happy because their water is kept clean. The plants are happy and grow quickly because they are receiving nutrients 24/7, and you should be happy and healthy having access to home-grown, organically produced food. The only external inputs to the system are electricity and fish food – however even the fish food can be system-grown.

How it Works - Detailed Explanation
You need not understand anything more than the layman’s explanation above in order to get started with Aquaponics. However, a little more knowledge certainly doesn’t hurt and will help you understand how the system works.
Aquaponics takes advantage of mother-nature’s own methods to convert fish waste into plant food. At the heart of this system is what is commonly referred to as the Nitrogen Cycle.

Nitrogen is an essential element necessary for life on Earth as we know it. The Nitrogen Cycle is a series of chemical processes whereby nitrogen from the environment is consumed by living organisms and processed into various different nitrogen-based chemical forms. This is accomplished via a chain of living organisms, each utilizing nitrogen in some way to live, and converting it into another nitrogen-based chemical structure which is then needed by another organism. In this way, nitrogen is continually cycled from the environment, through the biological system, and back into the environment.

This diagram illustrates the various stages of the overall nitrogen cycle in our environment. In Aquaponics, we are only concerned with a portion of this cycle, and we begin the nitrogen cycle at the Ammonium stage (NH4+) since that is what is directly excreted by our fish.
Fish waste, (NH4+), is taken advantage of and is the raw material from which plant food is produced. As can be seen in the illustration above, ammonium is only two chemical steps away from being fully edible plant food, or nitrate (NO3-). What it needs to be converted into nitrate is to be processed by two types of bacteria referred to as nitrifying bacteria. One type of nitrifying bacteria converts ammonium (NH4+) into nitrite (NO2-), and a second type of nitrifying bacteria converts nitrite into nitrate (NO3-).

Nitrifying bacteria are present almost everywhere in our environment, at some level, and they will be present, though at low levels, in any gravel used for grow beds. Once these bacteria start receiving ammonia-rich tank water on a regular basis, they will multiply and start converting ammonia into nitrite and then nitrate.
In a fully balanced system, which takes 6-8 weeks to develop, your grow bed bacteria will be producing tremendous quantities of nitrate. This will allow your plants to grow and will keep your fish water clean. Once this stage is reached, the system is said to be “matured,” and it pretty much keeps itself balanced, with very little maintenance required.

Aquaponics Advantages
  • Very low maintenance
  • Very high density food production. Regular plant-spacing rules don’t apply because roots do not need the room they need in regular planting.
  • Can be scaled to work in areas as small as apartment balconies to large commercial production facilities.
  • Produces plants as well as animal protein (fish).
  • Allows for very high fish stocking densities.
  • Uses very little water: once the system is going, you only need to replace water lost through evaporation and transpiration of plants.
  • All plant food and “fertilizers” are organically produced – by your fish. No need to deal with hydroponic nutrients or fertilizers, and more importantly, there is no need to be dependent on someone else’s production of these things (which by the way are a marvel of the oil age only).
  • Eliminates waste produced by aquaculture systems.
  • Avoids waste produced by regular hydroponic systems (including water waste).
  • In addition to the gravel grow-bed system, there are continuous-flow systems (aka floating-raft) for much higher-throughput and potential commercial or community-based production.
Potential Disadvantages
  • Moderate to high start-up costs. You’ll need a fish tank, at least one main pump as well as a power-failure back-up pump, grow beds, etc. You may also wish to enclose your set up in a greenhouse.
  • In very cold climates, you may have to heat your water. This could pose a serious disadvantage, but is surmountable.
  • Monitoring PH, ammonia, and nitrate/nitrite levels is very important and in the start-up phase (first 6-8 weeks) can be tedious as you’ll have to test daily. Once the system matures, levels of all these variables will stabilize and monitoring them becomes a weekly task done in under 20 minutes.
  • AP systems have one critical failure point, which is your water pump. A battery back-up system is required, otherwise your fish will all die due to lack of oxygenation upon your first significant power outage. These back-up systems are not complicated, but they do represent an additional expense.
Common Aquaponics Set-Ups
All AP systems must consist of a fish tank and grow beds. The differences between AP systems have to do with two basic design decisions:
  1. The first is how you choose to pump your water from the tank to the grow beds, and how you will drain it back into the tank after it has left the grow beds.
  2. The second has to do with the drain method used in each grow bed.
Grow Bed Drainage:

Grow beds serve both as a soil-less support medium for your plants and as a hosting medium for your bacteria. Grow beds will also attract and host worms and other organisms which contribute to the recycling of fish and plant waste into nitrates.

Almost all these organisms, and both types of nitrifying bacteria, require both water and oxygen to perform at peak levels. In fact, the bacteria we want cannot do without oxygen at all – their nitrifying function is fully aerobic. For this reason, it is necessary to introduce water into the system without also keeping oxygen out all the time.

Initially, it looks like this poses a problem. We want to be able to flood the grow beds and then drain them quickly. By flooding the grow beds, we ensure that water reaches every nook and cranny underneath the surface, leaving not an inch without water. By draining them, we introduce oxygen to the system, which is required by both plants and bacteria.

So, how do we do this without having complicated pumps and timers set up in each and every grow bed (all prone to fail)? The answer is provided to us by simple and elegant automatic siphons, which use only gravity and the laws of fluid dynamics to perform exactly the functions we need. They are automatic, they’ll function over and over again, are non-mechanical, consume no energy, and unless someone decides to start taxing gravity, function at zero cost.

The most common and favorite type of siphon used in Aquaponics is the Bell Siphon. Here is a video demonstrating one in action:

In our grow beds, we would construct the bell siphon so that it begins to drain water just before the water level reaches the surface of the grow bed gravel (about 5 cm below the surface). That is as high as we need to water to rise. Any higher will not help our plants in any way, and it will lead to algae forming on the surface of our gravel.

There are also loop siphons and other kinds of siphons out there, but the bell siphon is strongly preferred in Aquaponics, and is what I’ve used in my system.

The system by which grow beds are slowly filled and then quickly drained, on a continuous, cycling basis, is known as the “flood and drain” system, or also “ebb and flow” system. If you think about it, it really is a pretty good recreation of what we find in nature in regular dirt gardens – if only nature made it rain on a programmable, controlled basis, and if all our dirt gardens drained just perfectly all the time.

Tank, Bed and Pump Arrangements:

How we choose to arrange our fish tank and grow beds has a little to do with the size system being planned, available space, and the terrain we’re dealing with. Ideally, we want a system that is as simple as possible: one pump with no timers is ideal.

About the simplest system imaginable is to place a grow bed right on top of part of your fish tank, run the pump continuously, and allow the grow bed to flood and then drain straight down into your tank. There is, in fact, nothing wrong with this system, and it will work beautifully.

It is also easy to imagine expanding such a system to include more grow beds. All you need to watch out for is to keep the additional grow beds above the level of the tank so that you can drain the grow beds into the tank. The other key point to keep in mind is that your grow-bed-to-tank volume can range from 1:1 to 3:1, depending on your fish stocking density and the type of fish you have. That means one 1,000 liter tank could feed 3,000 liters of grow beds, at maximum fish stocking capacity, with say, a high-waste producing fish, such as tilapia.

Your fish tank water level will fluctuate as your grow beds fill and drain. If when you install your fish tank, you are unable to excavate and sink it partially or completely into the ground, you may find your grow beds are a little high for your liking.

Some prefer to drain their grow beds into a sump, before then pumping the sump water back into the tank. They also construct their tank so that it is higher than the grow beds, and allow the fish tank water to drain via gravity into the grow beds. This ensures constant water height in the fish tank, which may be important if you’re growing high densities of fish.

In a variant of this last system, the tank water is allowed to drain into the sump. From the sump, water is pumped both into the fish tank and into the grow beds at the same time. Murray Hallam has written about this system recently and highly recommends it. The advantages of this modification are that a) since the fish tank water is not delivered to the grow beds by gravity, the grow beds do not have to be absolutely level, b) by having the water pumped from the sump to the beds, you can install an inline valve on each grow bed, thereby allowing for disconnection in case of maintenance and for bed-by-bed regulation of the water inflow line.
Here are some pictures of different sized aquaponics systems:
Balcony Kit
Patio Kit
Family Sized/Homestead Kit
Aquaponics in a Bathtub
Commercial System
Commercial System
Silver Perch in AP System in Australia

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