Words: Sylvia Bernstein, www.theaquaponicsource.com

Ready for a revolution?

This article is the first in a two part series about aquaponics that will first describe aquaponic gardening, then focus on the practical details around the components of a thriving aquaponics system; from the fish, plants and bacteria to the grow beds, fish tanks and plumbing options.  Hopefully by the end of the next article I will have convinced some of you that aquaponics should be at least a part of your growing repertoire, and given you the tools you need to get started.

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 the foundation of great plant food.  At the same time, the worms convert the solid waste and decaying plant matter in your aquaponic system into vermicompost which supplies the remaining micronutrients.

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 as 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 considering 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, already years).
  • Best of all, you can say goodbye to pythium forever.  It is non-existent in aquaponics.

Types of Systems

AquaBundance by The Aquaponic Source

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 onto 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.

AquaBundance by The Aquaponic Source

Most media-based grow systems use a timer to turn the pump in the fish tank on and off.  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.  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.

Fish

Every aquaponic system starts with the fish and there are a wide variety from which to choose. The most important thing to keep in mind is to use freshwater fish. But which fresh water fish to raise?  To figure this out, start by deciding whether you want to grow fish for food or for show.  If you are interested in growing edible fish, tilapia are most commonly used in aquaponics because they are a tasty, fast-growing fish that have low oxygen requirements and aren’t very fussy about their aquatic environment.   Tilapia are generally purchased at fingerling size (3 – 4”) and take 9 – 12 months to reach “plate” size (approximately 12” and 1.5 pounds).  Many other edible fish can be raised as well, including trout, catfish, and perch.  Don’t be afraid to try other species.  Just be sure that  when you create your fish environment, you plan for optimal water temperature, sociability, and diet for which ever species you have chosen. Trout, for example, require a tank environment similar to the mountain streams from which they come.  This means water temperatures at 55° or below and plenty of oxygen.  They are also carnivorous, so it is impractical to grow other species with them or represent a variety of ages and sizes in the same tank.
After you have chosen your species, you will have to decide how many fish to put into your tank. The safest stocking density is one pound of mature fish for every 5 gallons (19 liters) of water.  This works out to roughly one fish for every 3 gallons (11 liters) of water, depending on the size of the fish.  Another good general rule of thumb is to have a minimum of 50 gallons of water to grow an edible fish to plate size.  If you are inclined towards keeping your fish as pets instead of food, you can go with a much smaller aquarium and use any freshwater fish you would adopt from a pet store.

Plants

People are growing almost every kind of plant in aquaponic systems.  The main exception is acid-loving plants, like blueberry bushes. The converted fish waste creates a near perfect, complete plant food that can be augmented if necessary.  Occasionally iron, calcium and/or potassium nutrient deficiencies show up but all can be corrected using small quantities of minerals that are safe for the fish (I have only supplemented once in almost 2 years of growing).
In an aquaponics grow bed, there is very little competition for food, water, and oxygen.  This means you can space plants much closer than you can in soil – up to twice as dense.  The only real consideration regarding plant density is competition for light in the canopy of the mature plants.  Make sure to plan for the ultimate size of each plant vs. its neighbors so that each plant will get the sunlight or grow-light exposure that it needs.   If you make a mistake, however, don’t lose sleep over it.  The root ball of an aquaponically grown plant tends to stay fairly compact, making most plants generally easy to move around even when they are mature.

When deciding what to plant, avoid cultivating too many of one type and age of plant in a single grow bed. A monoculture in aquaponics often leads to a simultaneous harvest, and harvesting many plants at once can put a system off balance.  Remember, your plants are filtering the water for your fish so be sure to keep a steady supply of seedlings on hand to replace harvested crops.

Consider companion planting to fight pests, as well.  For example, planting marigolds in your system can help ward away some insects.  If you do get a harmful insect infestation on your plants we recommend using insecticidal soap and/or neem oil as a safe, organic way to solve the problem quickly.  Do so carefully, however, because the fish aren’t crazy about having even organic pest controls in their water.  Avoid “bug bombs”, even if they are approved for organic use.

Beneficial Bacteria (Microbes) and Worms

Bacteria are the engine of an aquaponic system. Without nitrifying bacteria converting the ammonia to nitrates, the fish would quickly die from ammonia toxicity and the plants would starve for lack of nutrition.  Nitrosomonas bacteria convert the poisonous ammonia into nitrites and then nitrospira bacteria convert the nitrites into nitrates.  The process where the bacteria are naturally established is called “cycling”, and takes about a month. We will go into the mechanics of how to initiate and speed up cycling in a later article, but know that after becoming established, bacteria will colonize on all surfaces of the system that stay in contact with the fish water.

Be careful not to use chlorinated tap water when filling a tank, as chlorine will kill the nitrifying bacteria in the system. To remove chlorine from tap water, use a dechlorinating filter, or top off your tanks on a frequent basis with only a very small amount of water (less than 5% of the water volume), or establish a separate de-gassing tank.  Chlorine will “off-gas” (i.e. the chlorine leaves the water as a gas) on its own within a couple days, and more quickly if you add aeration.  Chloramine is also harmful to nitrifying bacteria and the fish and, if present, must be filtered from the water.  Contact your municipal water supply to find out if there is chloramine in your tap water.

Like a fine wine, the bacteria in an aquaponics system will get better over time—becoming more stable and effective.  It takes about a month to become established in your system but after 6 months it will outperform any traditional soil based or hydroponic system.  Be sure to treat the bacteria in your system like the precious friends that they are by never letting your grow bed dry out, never exposing the bacteria to freezing temperatures for an extended period of time, and never allow the bacteria to come into contact with chlorine or chloramine.

If bacteria are the engine of an aquaponic system, worms are its secret weapon.  Now the secret is out!  Add composting red worms to your media-based aquaponics system after a few months to break down the solid fish waste into vermicompost.  Vermicompost is extremely beneficial for the plants.

Next Issue

In the next issue of Urban Garden magazine we will go through what you need to know to build a media based aquaponics system, including grow bed considerations, fish tank considerations, plumbing how-to (timer, siphon, and flush valve), and considerations around the media.  The third article will conclude the series with instructions on starting up and operating your system – cycling and starting up the bio-filter, adding the fish and plants, operating your system and maintaining it, and hints on spotting problems.  My goal is that by the time we are done taking this journey together you will have the knowledge you need to start on an aquaponic adventure of your own.