It seems appropriate that we start our journey together by answering the question: What is aquaponics? At its most basic level aquaponics is the marriage of aquaculture (raising fish) and hydroponics (growing plants in water and without soil) together in one integrated system. The fish waste provides organic food for the growing plants and the plants naturally filter the water in which the fish live. The third and fourth critical, yet invisible actors in the play are the beneficial bacteria and composting red worms. Think of them as the Conversion Team. The beneficial bacteria exist on every moist surface of your aquaponic system. They convert the ammonia from the fish waste that is toxic to the fish and useless to the plants, first into nitrites and then into nitrates. The nitrates are relatively harmless to the fish and most importantly, they are great plant food. At the same time, the worms convert the solid waste and decaying plant matter in your aquaponic system into vermicompost.
Here is the rest of the story
- Aquaponic Gardening enables home fish farming. You can now feel good about eating fish again.
- Aquaponic Gardening uses 90% less water than soil-based gardening.
- Aquaponic Gardening is four to six times more productive on a square foot basis as soil-based gardening. This is because with aquaponic gardening, you can pack plants about twice as densely as you can in soil and the plants grow two to three times as fast as they do in soil.
- Aquaponic Gardening is free from weeds, watering and fertilizing concerns, and because it is done at waist height there is no back strain.
- Aquaponic Gardening is necessarily organic. Natural fish waste provides all the food the plants need. Pesticides would be harmful to the fish so they are never used. Hormones, antibiotics, and other fish additives would be harmful to the plants so they also are never used. And the result is every bit as flavorful as soil-based organic produce, with the added benefit of fresh fish for a safe, healthy source of protein.
- And if you are already a hydroponic gardener switching over to Aquaponic Gardening you can enjoy the following advantages
- Aquaponics has been shown to be more productive than hydroponics after the aquaponic bio-filter is fully established. (study by Dr. Nick Savidov, of the Crop Diversification Center South, Alberta Agriculture Food and Rural Development at Brooks, Alberta, Canada report in the “Aquaponics Journal,” 2nd Quarter, 2005)
- EC (electrical conductivity) tracking is replaced by tracking of Ammonia, Nitrite and Nitrate. Once your system is fully cycled you will only need to measure these about once a month or so vs. the much more frequent tracking of EC.
- pH is much more stable, again once your system is fully cycled.
- Fish feed is significantly less expensive than hydroponic nutrients.
- You never dump out your nutrient solution! Rather than having problems with chemical imbalance that you regularly experience in hydroponics, in an aquaponic system you are achieving a natural nitrogen balance that is the hallmark of a balanced eco-system. I view the water in my system as a critical component that I have nurtured into the near perfect balance at which it stays for as long as I choose to run my system (in my case…years).
- Best of all, you can say goodbye to pythium forever. It is non-existent in aquaponics.
Types of systems
Aquaponic systems can be created using a variety of hydroponic techniques, although systems that run-to-waste are not considered true aquaponics because they don’t close the loop by returning filtered water back to the fish tank. The most prevalent aquaponic growing methods are Deep Water Culture or raft-based, and Flood and Drain, or media-based. NFT and aeroponic techniques have also been used, but less widely and with limited success because solids from the fish waste – no matter how filtered – will eventually clog up the smaller tubing used by these system types.
Deep Water Culture (DWC) is where most of the university research on aquaponics has focused. This is especially true at the University of the Virgin Islands where Dr. James Rackocy has spent the past 30 years perfecting this growing technique. In DWC the fish are held in tanks separate from the plants. The solid fish waste is removed from the water using a settling tank and clarifying filters before it is sent on to the plant raceways. This prevents the plant roots from becoming coated with solid matter and suffocating. The fish water then circulates through a raceway that is covered with floating rafts. These rafts have holes in them to accept planted net pots whose roots dangle directly into the water. Newly planted rafts are dropped into the beginning of the raceway. The rafts progress along the raceway with each newly planted raft pushing the older rafts to the end of the raceway where they are pulled from the water and harvested. DWC is an excellent aquaponic growing technique for commercial growers because it is relatively easy to plant, tend, and harvest a large number of fast growing plants such as lettuces and some herbs. DWC also provides very stable water temperatures and pH levels because of the high volume of water required. The downsides of DWC are that in filtering the solids you lose many of the micro-organisms required to grow healthy, larger, fruiting plants. Also, while it has been done, it is difficult to grow larger plants to full size because of the challenges of getting enough oxygen to the larger root zone of a plant that lives its entire life in the water.
Most aquaponic home gardeners are using media based, flood and drain systems. A media based grow bed optimally has about 12” of either ½ – ¾” gravel (no limestone or granite!) or expanded clay (Hydroton). The reason for these extra deep beds is to enable a multi-layered environment that supports enough beneficial bacteria and composting red-worms to maintain a very stable bio-filter for your fish. It also gives you ultimate flexibility in what plant types you grow because you don’t ever have to think about the size of your root mass. Some gardeners are even growing subterranean plants, such as potatoes and carrots.
Most media-based grow systems use a timer to turn the pump in the fish tank on and off (some use a system
based on a siphon but how those work will have to wait for another article). A typical timer cycle is 15 minutes on followed by 30 – 45 minutes off and then the cycle repeats. When the pump starts, water from the fish tank is pumped into the grow bed. The grow bed fills with water up to about 10” or so. Obviously, this provides plenty of water and nutrients for the plants. Hydroton or other media above this height are in the “dry zone” and stay dry all of the time. When the water reaches about 10”, any additional water immediately returns to the fish tank through an “overflow” mechanism. The returning water strikes the water surface in the fish tank; thereby creating turbulence which helps aerate the fish tank water. When the timer turns off, the pump stops and the rest of the water in the grow bed returns to the fish tank. This period of inactivity gives the roots a chance to dry out and “breath” the air – something they greatly appreciate. Then, when the timer triggers the pump again the cycle repeats.
The remainder of the articles in this series will be centered on creating and successfully operating, a home media-based system. I will be approaching this sequentially as if you were building your own system and needed to know what to do first, then second, etc. (although you might want to consider purchasing an aquaponics system kit that has been manufactured for optimal performance, such as our Aquabundance System!) The next article will be about how to source a grow bed and fish tank, how to think about the ratio between the volume of these two pieces, what to consider in locating them, etc. We will then discuss plumbing and the water flow between the tank and the bed, followed by an entire article about fish. We have much to talk about!