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)
- 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.
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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, bell siphon or constant flow to regulate water through the media beds. In small aquarium sized systems, 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 the toip of stand pipe just below the surface of the media. Any additional water immediately returns to the fish tank through the standpipe 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 through the pump. 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.
Sizing your fish tank defines the ultimate size and flexibility of your aquaponics system, so consider the size early in your design process. If you are building a small, desktop system using an aquarium, you will be restricted to aquarium fish that will live comfortably in the size aquarium you own. If you want to grow larger, edible fish, the most important rule-of-thumb when choosing a tank is to make sure it is made of sturdy, food grade or food safe materials. Next, make sure that the tank is at least 18″ deep (457mm), and holds at least 50 gallons (189 Liters) of water. Tanks need to hold approximately 50 gallons (189 Liters) or more in order to grow ‘plate sized’ fish (12″ and 1 lbs, 300mm and 680g).
Aquaponics fish tanks can be made from just about any structure that fits the right dimensions and is lined with EPDM pond liner.
You can also use everything from recycled bathtubs, stock tanks, and IBC tanks, to recycled barrels.
Since your fish tank will be difficult to move once filled, you should carefully consider where you place it. Ideally the fish tank should be located indoors or outdoors in the shade. Fish don’t require sunlight to thrive and the extra heat and algae growth from sunlight could become a problem. Also, be sure the tank is on a solid surface that can handle the weight of the tank when filled with water. At 8.3 pounds per gallon, (or 1 kg per litre) you can easily reach a weight that might exceed the structural limits of the surface you are planning to use.
Wherever you choose to set up your tank, you will be well served to at least partially cover it to help prevent debris, children, and pets from falling in. Covering it will also lower the amount of light reaching the tank. This will help you keep control of the tank’s temperature and reduce algae.
Fish tank volume governs the maximize size of your grow bed. Here is why. The plants need the fish waste to thrive. The bigger the grow bed and thus the more plants, the more fish waste required. Simple – you need enough fish to support your plants. In general the recommended grow bed to fish tank ratio is approximately 1:1, i.e. the fish tank volume should be approximately equal to the volume of the grow bed. This ratio can also be thought of in gallons per cubic foot, striving for 6 gallons (22 liters) of fish tank to every cubic foot of grow bed. For example, a 50 gallon (189 liter) tank would be able to support 6 to 8 cubic feet of grow bed. You can extend this rule of thumb all the way to 2:1 (twice the fish tank volume to grow bed volume) but be sure to reduce the stocking density of your fish tank accordingly as this approach reduces your ability to filter the fish tank water with the grow bed plants.
Do not use metal containers, not even galvanized metal, for either the grow bed or the fish tank. Metals can quickly corrode, throwing your system off-balance by lowering your tank’s pH. Metal containers may also leach undesirable chemicals into your system. Copper and zinc are particularly dangerous for fish. An excellent choice is the AquaBundance Aquaponics Grow Bed.