By: Preston Coursey
Published: 15 តុលា 2014

This article is from ECHO Asia Note #22

[Editor’s Note: Preston Coursey is originally from Atlanta, Georgia. He graduated with a degree in geology with an emphasis in hydrogeology from the University of Georgia Southern. He currently lives in Chiang Mai and helps local Thais find resourceful and creative ways to enhance their own farming capabilities. He is currently researching aquaponics and green water technology, hoping to find appropriate and viable technologies for Thais to use in order to help them work toward self-sustainability.]

What is Aquaponics? In aquaponic systems, both fish and plants are grown. The fish are typically in a fish tank, and the plants are separated from the fish in a trough or grow-bed. The fish in the system provide nutrients to the plants, while the plants in the system filter byproducts from fish excrement out of the water, which can otherwise accumulate to toxic levels (Figure 1).

A low-cost concrete ring aquaponics system 1

Figure 1. Diagram of aquaponics systems. Used with permission from

After telling people this explanation, I am often asked, “So, do the plants eat fish poo?” The answer is no! Fish excrement is largely made of ammonia. A group of bacteria called Nitrosomonas spp. transforms the ammonia into nitrite (Figure 1). Another group of bacteria, called Nitrobacter spp., turns nitrite into nitrate (For more information about the roles of these bacteria, see: The plants in the system consume the nitrate, one of the most plant-available forms of nitrogen. In this way, the water is cleaned and can be reused without becoming toxic to the fish. Both Nitrosomonas and Nitrobacter bacteria occur in water naturally. They are extremely important and make an aquaponics system possible; without them, levels of ammonia would escalate until fish in the system would be harmed and eventually killed.

Even with the presence of Nitrosomonas and Nitrobacter, too much fish excrement in an aquaponics system will cause problems. In our larger raft system and rock bed system, we use filters to remove the larger, solid pieces of fish excrement. Too many solids can get caught in and start to cover the root structure of the plants, rendering the plants unable to absorb as many nutrients as they need. After some time, fish excrement solids can even start to clog drains and piping, creating flow issues. Using filters in a larger system will dramatically reduce these issues. For more information about some of these filtration systems, see www.backyardaquaponics. com.

The beauty of aquaponics is that you can build a system any way you want. In my experience, there are three common types of aquaponics systems. Elements of each type of system, described below, can be mixed and matched to create a hybrid aquaponics system.

1. Floating Raft System – This system has an open trough of water in which plants float on a raft (usually made of Styrofoam). The plants are typically in 1- or 2-inch cups that sit in holes drilled into the raft. Plants grow above the raft, while the roots are submerged in the water underneath the raft; the latter remove nitrate and filter the water, which is recycled to the fish.

2. Rock Bed System – This system is a trough system just like the floating raft system, but instead of open water, the trough is full of rock (typically river rock). With this system, seeds are planted directly in the rock and do not have to rely on cups. Typically this system works in conjunction with a bell siphon (which will be discussed further).

3. PVC System – This type of system goes by many names. We call it NRT, which stands for nutrient-rich technology. In this system, we use PVC pipes as the “grow beds.” The system looks a lot like the hydroponics systems that grow lettuce in pipes, which can often be found in greenhouses throughout the world. While both hydroponics and aquaponics systems produce plants, the nutrients to feed the plants in a hydroponics system come from organic or synthetic fertilizers dissolved in the water. In an aquaponics system, the nutrients to feed the plants come from the fish excrement. This PVC system requires the use of filters! If no filters are used, the big pieces of solid fish excrement will clog up the roots, reducing nutrient uptake and causing water flow issues throughout the system. In my opinion, the PVC aquaponics system is good for shallow-rooted plants such as lettuce, but not for long-rooted plants like tomatoes. If the roots are really long, they will travel throughout the system, clogging it and causing issues for other plants.

Our Farm

Currently, we have two 16 x 1 meter floating raft troughs, and one 16 x 1 meter rock bed that are connected to six 1 cubic meter fish tanks by PVC piping (elements 1 and 2 above). We also have three smaller stand-alone aquaponics units that we use as

A low-cost concrete ring aquaponics system 2

A low-cost concrete ring aquaponics system 3Photos of ECHO Asia’s aquaponics system (a hybrid rock bed and PVC system) and Preston’s aquaponics system (a rock bed system), respectively.

example starter units. One of our major goals is to help others understand how aquaponics works. We accomplish this by presenting aquaponics in a way that is easy to understand and replicate. Our Concrete Ring System, a rock bed system developed by Scott Breaden at his home and at the ECHO Asia Impact Center, accomplishes this goal. It has helped us cut down on building costs, simplified the system, and allowed us to use locally available materials.

How does a Concrete Ring System work?

The Concrete Ring System at our site is a small aquaponics unit that uses concrete rings with bottoms to hold water, instead of fish tanks or plant troughs.

The system at our site uses three concrete rings for the bottom (as the fish taks), and two concrete rings (as the rick beds) elevated on top of the bottom three. In the bottom of the system, the outer concrete rings are used as fish tanks. We are currently raising catfish in these tanks (see the fish section, below, for details and reasons). A PVC pipe connects all three concrete rings at the base of the unit, allowing water to flow between the three rings at the bottom and creating an equilibrium level among the three rings. We use a plastic fencing material at the opening of the pipes, to keep fish from swimming through them. In the middle bottom ring, a water pump transfers water from the bottom of the unit to the top. We use a 50-watt pump with a maximum head (height of water) of 3.0 meters and a maximum flow of 2500 Liters per hour.

The top of the unit consists of two concrete rings. We have filled these two rings with rock (see descriptions below); this is where we grow our plants. We have also installed a bell siphon in each of the top concrete rings. As the bell siphon starts to work, the water is sent from the top of the system back down to the bottom rings. A continuous water cycle is created as water flows from the top of the system to the bottom using gravity, then is pumped back to the top.

A low-cost concrete ring aquaponics system 4

Figure 2. A diagram of the Concrete Ring System.

Why We Built this Unit

Aquaponics can be a great alternative to farming or traditional gardening where land is limited, but starting an aquaponics unit can seem extremely complicated at first glance. We want to simplify aquaponics and enable individuals to successfully begin experimenting with it. In our quest for simplicity, we have focused on four areas: cost, material availability, size and relevance.

Cost is a major factor in sharing any type of technology; if the cost is too high, no one will be interested. Aquaponics often requires a high initial investment because of construction costs. However, one type of material that is very cheap in Thailand is concrete. It is locally available and Thais have a lot of experience working with concrete. In Thailand, you can buy concrete rings of all different sizes. Thais use these for planting trees, filtering water, and storing water. Thais even sell concrete rings with bottoms already on them, so they can hold water. By using these concrete rings, we have cut the cost of a small home-sized unit down significantly. The size of the unit is based on the size of the concrete rings, so this unit can be adjusted in size by using larger or smaller rings. The number of rings can also be customized. Our current concrete ring system only uses five rings, but the system can be expanded to use more. By keeping the system at the smaller size of five rings, we are keeping the system simple and easier to understand, while still showing how the system has the potential to be expanded.

Specifics of the System

Concrete Rings

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A low-cost concrete ring aquaponics system 6Photos: Top view of the Concrete Ring System.

For our specific system, we used concrete rings that are 80 cm (31.5 inches) wide and 40 cm (15.7 inches) deep. In Thailand you can buy them with bottoms, so they will hold water. They are usually waterproof, but we use a coal tar epoxy paint to help seal the ring. The coal tar epoxy also helps to prevent changes in pH caused by concrete (discussed later). This is the same type of material that is used to help protect boats from leaking. The coal tar epoxy we use needs to sit for at least two days before filling the rings with water or rocks.

Grow beds

We use the top two concrete rings of the system as grow beds. They are filled with river rock up to approximately 2 inches from the top of the ring. The water in the grow bed should only be allowed to fill to approximately 3 inches from the top of the ring, allowing the top layer of the rocks to stay dry. By doing so, you will cut down on the amount of algae that grows in your system. In our system, the height of the water column inside the grow bed is controlled by the height of the standpipe in the bell siphon (see below). In these grow beds, you can grow a variety of different vegetables, either planting seeds directly by hand, or growing seedlings on a tray and transplanting them into the system. We have had good success with tomatoes, lettuce, Chinese cabbage, cucumbers, peppers and Chinese kale.


We use river rocks, which are locally available in Thailand. I would recommend buying some type of river rock because they tend to be durable. For the most part, river rock is made up of quartz, which has a very stable molecular structure and does not erode easily. Other types of rock may break down and cause issues with your pump or fish. I would suggest buying rocks that are as big as your thumb, but smaller than your fist. These should be large enough to avoid any water channeling effects in your system, but small enough for seeds to successfully grow into your beds.


Many different types of fish can be used in an aquaponics system. We use catfish in our concrete ring system. They are easy to find in Thailand, and relatively inexpensive (five baht / $0.15 USD per fish). They are easy to take care of—they do not require an (expensive, energy-intensive) air pump, because they require little dissolved oxygen in water in to survive. Our bell siphon alone creates enough dissolved oxygen in our system for the fish to live.

Although catfish are easy to take care of, in other ways they can be difficult. I recommend buying younger, smaller catfish, because bigger ones will fight and kill each other for dominance when introduced to a new tank. Also, you will need to match your fish stocking density with the stage and capacity of your grow bed. [Ed: see EAN #20 for helpful information on stocking densities]. Finally, catfish like to jump out of their containers, so you will need to create a simple cover for your concrete rings. The cover can be anything from a plastic trash can lid to a fabricated cap, to plastic or metal netting, but just be sure it can be taken off and put on easily so that you can feed and harvest fish.

We feed the catfish store-bought fish feed that costs 550 baht ($17 USD) per 20 kg bag. It contains 32% protein, and we also use it with tilapia in a larger aquaponics system. Fish feeds contain different percentages of protein; you will need to find the appropriate amount for your fish. As the percent protein increases, the price of feed will increase as well. However, the lower the protein percentage, the less growth you will see in your fish, and the fish excrement will produce less nitrogen. In other words, fish growth and the amount of nitrogen in a system are proportional to the amount of protein in the fish food you are using. Take note that fish can only absorb up to a certain percentage of protein in their feed. Tilapia, for example, cannot absorb all the protein in a feed that is higher than 32% protein. Pick the correct type of fish feed for the species of fish you want to raise. [Editors’ Note: See ECHO Asia Note #20 for more information and ideas about creating your own on-farm fish feeds.]

Ours is a small system used only to educate others about aquaponics, so we are not interested in harvesting fish. Because of this, we give the fish only 50 grams of food per day for the entire system. As a rule of thumb, if the fish have not eaten all of the food in five minutes, you are giving them too much feed. The more you feed the fish, the more excrement they will produce, and you will need either a more intense filtration system or plants that can deal with more nitrogen (larger plants require more nitrogen).

Here is a great video for understanding which fish to use and what type of food to use:

Bell Siphon

Our concrete ring aquaponics system has some technical parts. For example, we use a bell siphon, both to provide adequate moisture for the growing medium and plants in the medium, and to ensure there is oxygen in the root zone. Also, by allowing air to reach the lower parts of the concrete ring, we discourage anaerobic bacteria from growing and causing issues in our system. Here is a great blog to help you

A low-cost concrete ring aquaponics system 7

A low-cost concrete ring aquaponics system 8Photos of the bell siphon.

understand bell siphons and their benefits over a flood and drain design ( siphons/). Here is a link to a great video that will help you understand how bell siphons work ( =lyrvcCqv5V0).

Take the time to understand how a bell siphon works. At our site, we use a bell siphon with a 1-inch standpipe and a funnel at the top, to help with small changes in flow rates. The height of the standpipe will determine the height of the water column inside the concrete ring. The standpipe should be at least 2/3 the height of the concrete ring. The bell, or outside pipe, is made from 2 ½-inch PVC pipe with a cap. The standard rule for bell siphons is to always have a 1:2 ratio, so if the standpipe is 1 inch, the bell must be 2 inches. However, we use a 2 ½-inch bell to accommodate the funnel on the standpipe. Also note that the bell must be at least 2 inches taller (measured from the inside of the bell) than the standpipe and funnel inside the bell. If it is not 2 inches higher, the bell siphon will not work. Finally, for a successful bell siphon, the outflow pipe (the piping underneath) needs to have an elbow, or trap. The elbow helps restrict the outflow flow rate, which will help the siphon activate. If you do not want to use an elbow, you can use a straight pipe restrictor to achieve the same effect. See for information on how to build a type of bell siphon.

We installed a guard around our bell siphon. The guard is a 6-inch PVC pipe, cut to fit around the bell siphon. We drilled holes into the pipe in order to allow water flow, but keep rocks out. The guard helps protect our bell siphon from being clogged by plant roots. We use a 6-inch PVC pipe because it is easy to stick a hand inside and pull away roots that may be clogging the bell siphon.

Bell siphons are very useful, but can also be frustrating. I have had several issues with bell siphons in the past, and I created a list of what to consider when troubleshooting a bell siphon:

Problem 1: The bell siphon will not start siphoning

• Is your flow rate high enough? If it is not high enough, the water will just drain and not start the suction process.

• Are the bell and standpipe level? Generally the more level your standpipe and bell are, the fewer issues you will have. If the bell does not stand up straight, use a string or other mechanism to help secure it.

• If your bell siphon has been working for a couple of months and suddenly stops working, you probably have some flow restriction issues. After a system runs for a while, fish solids can stick to the sides of the pipe, restricting flow. Typically in this case you will need to clean out your pipes or replace the pipes coming from your water pump with bigger pipes.

• Take out the bell and see if there are any roots growing into the bell siphon, which will restrict water flow into the siphon.

Problem 2: The bell siphon will not shut off

• Typically this means that there is too much water flow. You should always have a valve installed on the pipes coming from your water pump, to control water flow through the system.

• I have known some rock systems to have water-channeling issues. This results in the bell siphon turning on and off rapidly. If you use gravel that is too small, fish excrement will stick to the rock and create localized channeling. One solution is to clean your rocks. A better solution is to replace your rocks with bigger rocks.

Water Pump

For a five-ring concrete ring system like ours, you can use a water pump that is

A low-cost concrete ring aquaponics system 12

A low-cost concrete ring aquaponics system 13A low-cost concrete ring aquaponics system 14(Top and Middle) Photos of the water pump and piping from the pump to the grow beds. (Bottom) Photos of the drain system.

between 35 and 50 watts. A 35-watt pump can provide enough flow for the bell siphon (1 inch stand pipe) in the system to work, but if there is anything restricting water flow, you will start to have issues with the siphon. I would recommend using a 50-watt pump for a five-ring system. When you connect your pump to the system, make sure you use PVC pipes bigger than ½ inch in diameter. The ½-inch pipe will have issues with fish excrement sticking to the sides of the pipes, restricting flow over time. I would also advise against gluing the PVC that connects the pump to the top of the unit. If you use glue and then have any issues or want to reorganize your setup, you will not be able to change anything without rebuilding the system. Currently, our pump runs 24 hours a day, seven days a week, but you can use a timer if you are working with catfish (because they don’t need dissolved oxygen).

Sun Protection

Some type of shade is important for this concrete ring system. If the unit is in direct sunlight all day, the water will get too hot and cause the plants to wither. During the hot season here in Thailand, most days easily reach over 95°F (35°C), which is challenging for plants and fish in an aquaponics system. We constructed a frame from bamboo and hung a shade cloth above the plants to protect them from the sun, but most days during our hot season in Thailand, it was still too hot and they wilted during the day. However, they usually perked back up at night when it started to cool a bit. If you live in a country with similar very hot temperatures, I suggest building the unit in an area that is shaded during part of the afternoon. In an aquaponics system, sun protection also benefits the Nitrosomonas and Nitrobacter bacteria, which are extremely sensitive to sunlight. In addition to a shade cloth over the entire system, we also use shade cloth to cover the bottom rings of the unit.

Bottom Flow

We raise catfish in the two bottom outer rings of our system. These two rings are connected to the center ring, where the pump is located, by 2-inch PVC pipes that have been cemented into the walls of the concrete rings. 2-inch PVC pipes allow the water to flow through the system unrestricted. We also have a porous cover over the 2-inch pipe opening, to keep our catfish segregated to the outside tanks. Because the center ring is open to the air, it is important to have some type of mosquito control; in our case, we use guppies that eat mosquito larvae. We allow the guppies to swim from ring to ring. [Editors’ note: in the system at the ECHO Asia Impact Center, our “sump” ring, i.e. where our pump is located, contains a healthy population of guppies for mosquito control, as well as a covering of water ferns. The latter provide food for the guppies to eat, help clarify our water, and are an excellent protein source, if you are interested in making your own fish food (See EAN #20 for more information about the use of water fern).]


We installed drains in all our concrete rings. These are necessary when we have to do any type of “deep cleaning.” We use 1-inch PVC pipes with valves that drain into a nearby area. If you install similar drains, I suggest that you have them drain into an area where you can collect the water. This water is high in nitrate and can be used on a garden as a natural liquid fertilizer.


Since our system is a rock bed system, filters are not totally necessary. However, for our system we do use a very small filter. We cut off the bottom of a 4-inch planting cup, then placed an easily-removable sponge-like filter material inside. We placed the filter under the water inlet in the grow bed, where it catches excrement solids and reduces splashing from incoming water, thus reducing algae growth. We wash the filter daily, to take some of the excess excrement away from the system. Too much excrement may cause your rock to fill up with solids, which will block water from flowing to all parts of the grow bed, thus creating channeling issues. (Author’s note: most water pumps bought at fish shops will come with a filter inside of them. In my opinion, the filter should be taken out. If left in, it can easily fill up with excrement and the pump will not work as well, thus causing your bell siphon not to work. The filter can be taken out and even used in the small filter mentioned above.)


The amount of cleaning an aquaponics system will need depends on the type of system. If you are using filters in your system, you typically won’t have to clean your system for a couple years. Our concrete system has to be cleaned about four times a year. In our system, we currently have about 20 adult catfish that we feed 50 grams of food every day; if you are giving more than that, you may need to clean your system more often, depending on the amount of solid fish excrement in the system. Cleaning the system is not diffi-cult, if you have drains installed. Be sure to move your fish to a temporary tank or bucket before cleaning your system. When it is time to clean, just open the drains. After running the unit for some time, the bottom rings will fill up with fish waste. When cleaning your system, make sure you stir up the fish waste so it is suspended in the water that is drained out of the system.

pH Control

Typical aquaponics systems usually have a pH range between 6 and 8. Using any type of concrete will cause the pH in your system to change drastically, potentially creating issues that could be detrimental to the health of your fish and plants. This problem can be solved in a couple of ways. We use coal tar epoxy to paint the inside of our concrete rings (discussed above). This is expensive to use, but you only need it for one application. If you prefer not to use coal tar epoxy, local Thais instead will cut up the trunk of a banana tree, put it in the concrete ring with water and let it sit for two weeks, which will neutralize the pH. This is a very successful method of neutralizing pH, but we used coal tar epoxy instead because we did not want to wait two weeks.

Getting Your System up and Running

When you first start your system I would suggest using only about 10 fish. As discussed earlier, the bacteria groups that convert ammonia to nitrite and nitrite to nitrate are extremely important for a successful aquaponics system. These bacteria groups occur naturally in water, but develop slowly. The older your system is, the better it will begin to work, because there will be more bacteria to create the nitrate you need. Your system may not be able to handle more than 10 fish in the beginning. After a month or so, you can start raising more fish.

As far as what to grow, I suggest starting with a vegetable that is easy to grow and does not demand a lot of nutrients. Remember, younger systems will not contain as much good bacteria as an older system, and thus will have fewer available nutrients. For systems that are started in Thailand, I always suggest to grow morning glories, since this vegetable seems to be able to grow anywhere. After about a month, you should be able to grow more nutrient-demanding vegetables, such as tomatoes. As we learned earlier, in an aquaponics system, plants help fish and fish help plants. There should be an equilibrium between the number of fish you have and the number of plants you have. Aquaponics is all about balance, so if you have a lot of fish, then you should have a lot of vegetables (or more filters). That said, in my experience, the real issue is not how many fish you have, but how much you feed them. When you first start your system, I would recommend testing your system for ammonia, nitrite, and nitrate. Test kits for ammonia, nitrite, and nitrate can usually be found at most fish shops. If you see that your ammonia or nitrite has spiked to over 1ppm, then simply stop feeding your fish for a couple days (fish can live for several days without food).

The amount of feed you use will depend on the purpose of your system. For example, if you are more interested in harvesting plants than harvesting fish, you won’t have to feed your fish very much everyday. You will just need to feed the fish enough to have a healthy amount of nitrate in the system. Here is a great article if you want to learn more about feeding ratios and general guidelines of aquaponics:

Safe Ways to Test Additives

An aquaponics system does not use soil. While there are some benefits to this, including a cleaner harvest and no need to till land, there are also some disadvantages. One major disadvantage of aquaponics is that some minerals that are naturally present in soil will not be in the water of the system. For example, iron is needed by most plants. It is not naturally found in an aquaponics unit, because the fish do not provide iron to the system. You will have to buy the appropriate type (usually chelated iron) and add it to the unit.

Any type of additive or pest control used in an aquaponics system must be totally organic, or your fish and/or plants may die. So, how do we know what we can put into the system? There is a way to test if what you hope to add is safe. Place a few of your fish in a container separate from your system, and connect it with an air pump. Then add half the concentration of the additive you wish to have in your system. Leave the fish in the tank for five or more days. If they survive, add double the amount of the additive. If the fish are still alive a week later, the additive is safe to use. Do not add anything that will change the pH of your system drastically, because aquaponics systems are very susceptible to swings in pH.


The cost of creating an aquaponics system will depend on the design of your system, the cost of materials, and the cost and usage of electricity, fish, and fish feed in your area. To give an idea of some of the affiliated costs, here is a table showing construction costs for two different cement ring systems created in Northern Thailand.

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A low-cost concrete ring aquaponics system 16

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Aquaponics is a wonderful new technology that can be customized in many different ways. However, a successful aquaponics system will require daily management and basic knowledge of water chemistry. It will also involve a good deal of trial and error. As you experiment with aquaponics, you will tailor your system to fit your specific needs. The world of aquaponics is new, but growing fast. Setting up a smaller unit is a great first step into learning about aquaponics. Our concrete ring system design provides an excellent and cheap opportunity for someone to try their hand at aquaponics!