An old man I met once told me this story:
One day—for some reason—four blind women were feeling what the old man had told them was an elephant.
Not knowing what an elephant was, the one feeling the leg said, “It feels like the base of a tree.”
The one feeling the trunk said, “It feels like a large snake.”
The one feeling the ear said, “It feels like a big leaf.”
The one feeling the tusk said, “It feels like a spear.”
“No,” the old man replied. “I told you it’s an elephant.”
Then, some ants on the tree attacked the first woman, the snake bit the second woman, the leaf gave the third woman poison ivy, and the fourth woman chased after the old man with the spear.
In the same fashion, I’d like to tell you about five different types of aquaponic systems. Like the different parts of a fake elephant, each can bite you if you get bad advice. This article is primarily about backyard systems, which differ in important ways from commercial systems.
So, without further ado, these are the five types of aquaponic systems commonly used by backyarders:
- Constant height one pump
- Deep water culture
- Vertical growing
- Alternating flood and drain
Constant Height, One Pump
The constant height one pump (CHOP) method consists of a fish tank, sump tank and one or more grow beds filled with growing media such as gravel. A popular version of this method includes The IBC of Aquaponics, a free design built using a 275-gal. international bulk container.
In this system, the single pump runs all the time, pulling water from the sump into the fish tank, which drains into the media-filled grow beds where the plants reside. Each grow bed contains a bell siphon.
Water flows into each grow bed and rises until it reaches the top of the bell siphon, then flushes into the sump like a toilet. Many online designs teach you to make bell siphons yourself, but this is a bad idea. Bell siphons are touchy. Spending a bit of money on a proven product will pay itself back in therapy bills in no time.
In the CHOP system, the media beds perform nitrification (convert the liquid waste to nutrients), and solids filtration and mineralization (convert the solid waste to nutrients). Many people also include worms in their media, as they help break down solids. Regardless, media beds fill up with solids over time and have to be cleaned.
One option is to include a solids filter before the media beds, which lengthens this maintenance cycle. The upsides of the CHOP system include its use of inexpensive materials, its reliability and its ability to be insulated and air-sealed (see my Aquaponics for the Frozen Tundra series in Maximum Yield’s January-March 2015 issues for more on this).
The one major downside of the CHOP system is you need a large sump tank that is able to hold as much water as all the grow beds combined. The sump should not contain fish because at some point all the water will be in the grow beds at once, leaving the sump empty and the fish flopping around. This extremely large sump tank also provides additional surface area from which to lose heat in winter.
Alternating Flood and Drain
In the alternating flood and drain (AFD) system, the growing area is divided into 4-8 media-filled grow beds. The pump floods each bed alternately use a device known as an aquaponics indexing valve. Note that irrigation indexing valves won’t work at low pressures.
The pump in an AFD system is run by a timer. As the timer turns on, the pump supplies water to the indexing valve, which sends it to one grow bed equipped with a small drain and large overflow. When the timer stops, the water drains back to the fish tank and the indexing valve indexes to the next grow bed so you only ever have to supply a portion of the water at any one time. Like CHOP systems, the media beds provide nitrification and solids filtration and mineralization through the use of worms.
The AFD system allows for tight insulation and air sealing, avoids the need for a sump tank and allows you to slow down the timer frequency at night to save pumping and heating energy. Disadvantages of this system include the need for a reliable and powerful pump, a small filter to collect things like small sticks that could block the indexing valve and some additional plumbing.
Deep Water Culture
Originally designed for commercial growers, deep water culture (DWC) has recently begun to take hold with backyarders. A free design called the Zero to Hero Aquaponics System is available online, with listservs for most major cities of people building and operating them.
In DWC, water drains from the fish tank through a series of filters into the water-filled grow bed. Plants sit in sheets of insulation, floating or supported above the grow bed. The pump can either reside in the grow bed or in a small sump below, and moves water back up to the fish tank.
The filter system typically fits between the fish tank and the grow beds, keeping the grow beds clean. It can include a nitrification filter, a swirl filter or clarifier, and a suspended solids filter. Some growers add freshwater shrimp such as scuds to further clean their grow beds. Others use prawns, though these are territorial creatures and are prone to defend their honor in elaborate duels.
The DWC system allows for a small and inexpensive pump and it lets you keep your beds flooded, which prevents air from being expelled during flooding and sucked back in during draining. This saves heat by avoiding evaporation in winter. The primary disadvantage of DWC is that the solids filters require some labor—usually about 15 minutes once a week. The grow beds eventually gather solids and must be cleaned as well, though this is much easier than with media beds.
Popular with big-city rooftop and indoor growers, vertical growing is catching on with backyarders as well. In addition to prefab grow towers, several online designs explain how to make DIY vertical gardens from PVC pipe. It’s trippy to walk through a commercial greenhouse full of these, especially in the dark. I’d love to see a horror movie set in a large, multi-story vertical growing facility.
Like media-filled grow beds, vertical towers can perform nitrification, solids filtration and solids mineralization without the need for separate filters. However, like media beds, they also require cleaning.
Vertical growing optimizes space, which is crucial in an urban environment or heated greenhouse. It achieves this by maximizing both vertical and horizontal space, filling it with multiple rows of towers.
From a cold-climate perspective, growing more in a smaller space saves on heating costs. Disadvantages include the need to run small drip tubing to each tower that can become clogged with fish waste, the near-impossibility of insulating or air-sealing the towers, the need for a sump tank and the challenge of providing sufficient light to each plant.
Like hybrid cars that combine multiple types of motors to propel your car down the road, hybrid aquaponic systems combine multiple types of growing and filtering systems to propel fish and plants into your mouth. Here are the most common hybrid approaches:
- CHOP or AFD system that drains into a DWC bed, then into a sump
- Vertical growing system that drains into a DWC bed
- Vertical growing system that pulls from the same fish tanks as another system (can be used seasonally)
- DWC system with filters that collect solids for use on soil gardens elsewhere
Options 1 and 2 use a media-filled grow bed to provide nitrification and solids filtration and mineralization. This allows you to use a DWC bed without the requisite filters. It’s important to size your media-filled bed to provide the full filtration function. A website called Aquaponic Solutions provides free calculators for sizing media grow beds.
Option 3 is an example of a system that can be run differently in summer than in winter using a poorly insulated or light-intensive growing system in the summer and shutting it off in the winter. This can work well with fish that zonk out for most of the winter and produce fewer nutrients.
Option 4 works exceptionally well as a disposal mechanism for spent fish solid waste and plant roots. Even after use in aquaponics, solid fish waste contains organic material and nutrients that can do wonders for your soil garden.
Any of these aquaponic systems will work well, depending on how well you build and maintain them. A well-designed system works like a Ronco rotisserie—you set it and forget it. But a poorly considered system can compromise your sanity as everything breaks, leaks and overflows almost constantly.
Having experienced both of these scenarios, I encourage everyone building their first aquaponic system to use a tried-and-tested design, such as those mentioned here, without making any modifications.
Once you’ve learned the ins-and-outs of a system’s operation, you’ll be in a great place to experiment with hybrid systems and other innovations. And remember, watch out for that old man and his “elephant.”