How to Design and Build an Aquaponic System

An aquaponic system is best described as a hydroponic system where fish are added to the system to produce the waste products where it is converted, by bacteria within the system, to nutrients needed for the plants.

There are many variations of aquaponic systems.  As you can imagine, there are systems that you can build yourself for around $200, to systems you can purchase for thousands of dollars.  The choice of design and the size of the system all depend on your goals, and the purpose of the system.

At our home, I have put together three systems which follow the most basic form of Aquaponic system design, but are slightly modified to accommodate the slightly varied needs of each system.

The most basic Aquaponic system consists of a large fish tank or pond, a water cycling system, and the grow bed.

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As can be seen in the attached photo, this type of system is a closed system where only fish food and occasional water (used by the plants and evaporation) are added as needed.  Although the photo shows an enclosed system, there are many details that are not seen and need to be addressed when you set up your system.  Following sections will go through each component of the system and will address issues/challenges you might face when setting up your system at home.

Fish Tank Set-Up

This is the nutrition factory of your aquaponic set up and I personally believe it is the most important part of the system.

To design your fish tank, you have to first decide what size of a grow bed you want to have.  Here is the basic rule of thumb: for every square foot of grow bed, you need two fish.  For every fish, you need 5 gallons of water.  For example, if you want to have a 3’x5’ grow bed, you need to have 30 fish.  For 30 fish, you need at least 150 gallons of water.   Based on these numbers, you need to design a tank that has at least 175 gallons volume (25 gallons extra is for the water to be a few inches below the rim and prevent splashing, or fish jumping out).  Make sure your fish tank design is at least 18” deep.  This helps the fish feel safe, stay out of the reach of most predators, and to allow them to change their depth during water temperature fluctuations.

Once you have designed the dimensions of your fish tank, you are ready to build it.  But before doing that, you need to decide where it is going.  This is important because this tank needs to be out of direct sunlight, away from wind and dust paths.  Direct sunlight, wind, and dust will cause your water to go bad quickly, resulting in extra maintenance work for you.

Before building the tank, remember water is heavy and will create a great deal of pressure against the walls of your tank.  In my tank designs, I have always used ½” thick plywood with 4 vertical 2”x4” supports, and a lip/rim made of 2”x4” studs.  The length of the vertical supports is determined by the type of the grow bed you will be building.  Before cutting these vertical supports, please see the section describing the two types of grow beds.

Once the tank is built, the interior of the tank is then lined with reinforced Pond liner.  You can buy pond liner from your local Do it yourself store (Home depot, Lowes, etc.).  Make sure the pond liner sits snug against the walls and corners of your tank, and comes up and wraps around the lip of the tank.  This will help keep water away from the wood, and will make your tank last a lot longer.  To protect your wooden tank even more, you can use Clear Coat to seal the wood before putting the liner in place.  Make sure the Clear Coat is fully dried before you put the liner in place.  I use staples to hold my pond liner in place.  All staples must be placed at the edges of the pond liner where it wraps around the lip of the tank.  Any staples placed in the water or in the path of water, will allow moisture to come in contact with the wood, therefore causing wood rot, mold, and fungus growth.

Once you have completed the tank, you need to fill it up with water and let it sit for at least two to three days.  This will get rid of most of the chlorine and other additives in your tap water.

Next step in setting up your fish tank is Water aeration and cycling system.  In my set up, I have used a fish tank air pump for 70 gallon tank which has two outputs.  You can attach a large air stone to each output, or use a valve or diversion system to allow for more air stones.  With each pump, I use two 6” air stones which provide plenty of air for the 150-250 gallon systems.

Once you have put in your air pumps and air stones, turn the pump on and allow it to aerate the tank for at least a day before adding any fish.

I highly recommend you add some test fish to the pond before you add any of your actual, most likely expensive, fish.  I always add a few feeder gold fish to the water before adding my Tilapia (some systems use catfish, trout, perch, etc.).  You can buy them for about $0.10 each.  This will not only test the readiness of your fish, it will also add some beneficial bacteria to your water.  These bacteria are the ones responsible for turning your fish waste into nutrients usable by your plants.

Setting Up the Grow Bed:

Next step in the process is building your grow bed.  Your grow bed can be built as a stackable unit sitting right on top of your fish tank (as shown in the photo above), or a stand-alone, sitting away from your tank.  There are pros and cons to building your bed on top of your fish tank.  One of the advantages of such a system is that it provides a shaded area on top of the tank.  This is very important in warmer climates with plenty of sunshine.  It helps to keep the water cooler, and it prevents rapid growth of Algae.  Another advantage of this set up is the fact that a stackable system maximizes the use of your space and reduces the footprint needed for any system.

If you are going to build a stackable system, you need to cut the length of the vertical supports so that it allows at least 16” of clearance between your tank’s top and the bottom of the bed. This is important for feeding the fish as well as observing the health of your tank. The bed going on top of the pond, depending on the type of the bed you are going to build, should be at least 4” deep.  The foot print of your grow bed was already determined at the beginning stage, when you were designing and building your fish tank.

Beds filled with gravel, timed water flow, and constant drainage need a minimum of 4” depth.  I use this type of setup.  Such systems are fed using a timer to pump the water into the bed at preset intervals, allowing the water to drain at a constant flow.  The time between the watering intervals allows the bed to completely drain, letting the roots absorb the much needed oxygen.

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Beds designed for constant water flow (NFT, or deep flow) need to be set up properly to ensure plant roots receive the proper amount of nutrients as well as oxygen.  This type of setup can be a bit tricky and need occasional adjustments to ensure proper balance between feeding and oxygen intake of the plants.

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Whether you are building a media filled or another style of grow bed, you need to make sure your beds are sealed against moisture and water intrusion.  I made all my beds using the same material as my fish tank, then lined it with pond liner and stapled the ends of the liner the same way as my fish tank.

In addition, the bed must have a slight slope starting from where the water enters the grow bed towards the water drainage area.  A rule of thumb is 1” drop for every two feet distance between the water inlet and the drain.  If you are building a media filled grow bed, this is the time you can fill it with gravel or any other type of media suitable for Aquaponic system.  Make sure you wash your media before filling the grow bed with it. Fill the grow bed to about an inch from the top.

After you have finished building your grow bed (and filled it) it is time to start thinking about the water pump you are going to use.  The size of the pump is determined by your grow bed size, and the number of plants it will be hosting.  To provide the proper amount of water needed, and to reduce the pressure on my water pump, I use an adjustable flow 200 GPM (Gallons per Minute) submersible pump for each of my 3’x5’ grow beds.  This allows me to adjust the amount of water delivered based on the temperature, season, the number of the plants in the bed, and the size of each plant.  The submersible pump also allows me to keep the pump in the tank and away from foot traffic.

The water cycling system I use is composed of a submersible pump, tubing for the pump output, ¾ PVC valve, and ¾ PVC pipes, fittings, and connectors.  Water pump is connected to the ¾” PVC valve via a drip-irrigation black tubing (the tube size depends on the output size of your pump).  The PVC valve is then attached to my watering wand.  The watering wand is made of a ¾” pipe with 1/8” holes drilled along its length at 6” intervals.  The length of this pipe is usually 6” longer than the width of my grow bed.  The location of holes start at least 6” from each end of the pipe.  For example, for a 3’ wide grow bed, I cut a 3’ 6” pipe, mark the first hole 6” from the end and every 6” from there on, with the last hole 6” away from the other end of the pipe.  I then put an end cap at one end, and connect the other end to the PVC valve.  When installing the pipe onto your bed, you can secure it in place with 1” electric pipe straps.  Make sure you don’t glue the pipe pieces together.  This will allow you to adjust the tilt of the location of the holes on the pipe in respect to the grow bed surface.  The set up described here also increases the aeration of water fed to the bed.  This watering system can be used for other grow beds as well.

Adding fish to the system:

Now that you have built the fish tank, the aeration system, the grow bed, and the water cycling system, and you have checked the health of your fish tank, you are ready to load your tank with the fish.  The type of fish you use depends on your environment, and your personal reference.  There are many types of fish which are available for this type of system. My personal preference is Tilapia.  They are hardy fish and grow very fast. The down side is that they are warm water fish and as a result are not suitable for cold climates.   Following photo shows some of the fish types suitable for an Aquaponic system:

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Expanding your Aquaponic system:

Once you have run your system for a few weeks, your fish have grown to a semi adult size, and the bacteria levels in your system have reached a healthy level, you can increase the size of the grow bed attached to the system.  This can easily be done by adding a second or even third bed to your system.  When doing so, keep in mind that there is only a certain amount of nutrients your system can produce.  Be careful how much growing area you add to your system.  The size of the new beds depend on the maturity of your system and the type of plants you will be growing.  Make sure you don’t ever tax your fish tank.  If you do so, your plants will not be healthy, and their yield will drop dramatically.  My recommendation is to start with one grow bed filled with appropriately spaced plants.  One the system has established, add a second bed with a few plants.  If everything goes well, add a few more plants every three to four weeks till you see signs of stress in your plants.  At that time, you can either harvest some of the older plants, or remove the latest batch of plants added to your system.  This will take time, but once you have dialed in the optimum set up for your system, you’ll be enjoying the rewards your har work and patience.

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