Aquaponics is a sustainable, decentralized method of food production that merges aquaculture and hydroponics. It’s cheap to build and maintain, can be done in a small space indoors or outdoors, requires no weeding or digging, tolerates denser planting, and all the water is recycled in a closed, regenerative loop. The only water that needs to be replaced is what’s lost to evaporation and by the plants, and the only necessary inputs are sunlight and fish food. It is also expandable, allowing you to add grow beds, fish tanks, a filter, or a sump tank later on. However, it can be complicated, requires more work up front, can have high set up costs, and requires time for maintenance, not to mention lots of patience, and a high tolerance for failure and experimentation.
Aquaponics offers a viable alternative to traditional, monocrop agriculture. Monocroping is a method of growing industrial quantities of a single crop in one area, and then selling it and shipping it to far away locations. This is an intensive, resource-draining, pollution-heavy, and destructive process that’s bad for the environment and for human livelihood and well-being. By contrast, aquaponics produces fish and vegetables year round with no pollution or runoff. It is completely organic, needing no chemicals or fertilizers, and utilizes intensive planting methods that yield 150-200% more produce per square foot, while using between 90-95% less water compared to traditional, monocrop agriculture. This allows greater access to locally grown foods, reducing our reliance on imported goods that are costly to produce, preserve, and transport. You can even sell excess produce to restaurants, private individuals, buyers clubs, community supported agriculture (CSA) boxes, or farmer’s markets.
How It Works
Aquaponics works by creating a self-watering system that uses fish effluent and plants in a self-reinforcing environment to grow plants at an accelerated rate. The mutual interconnection of the plants with the fish replicates a symbiotic relationship in nature, cultivating fish and plants in a recirculating mini-ecosystem. Fish produce ammonia-containing waste in the tanks, which is deposited (either by a pump or by gravity) from the tanks into the grow beds. Inside of these beds are held a solid, hydroponic support medium, which houses bacteria and micro-organisms. The water distributes itself through the rock media, which acts as one layer of filtration, and is then drained at short intervals.
The solid support media provides structure for the plants to grow, and also acts as a proliferation area for a series of aerobic, nitrifying bacteria.
One of these micro-organisms, Nitrosomonas sp., converts the nitrogen and ammonia in the fish waste into nitrites. Another species, Nitrobacter sp., then converts the nitrites into nitrates. Compost worms could also be used to eat food scraps and provide added fertilizer. The plants absorb these nitrates, convert them into food, and pick up the materials in the water and help to clean and filter it out. The water then gets siphoned out of the grow beds and is returned to the fish tank.
- 1x quiet-flow pump, 400-800 gallons per hour
- 2x 55 gallon drums
- 2x 10 ft. sections ¾ in PVC pipe
- 1x ½ to ¾ in. male to PVC union
- 2 1/2 in. screws
- 1 in. screws
- 2x wood braces
- 1x ¾ in. Tee
- 2x ¾ in. 90-degree elbows
- 1x 10 ft. section of 1 in. PVC pipe
- 4x 1 in. 90-degree elbows
- 2x 1 in. Uniseals or bulkhead fitting
- Power drill
- Jig saw w/ PVC blade
- 1 ¾ in. hole saw
- 1 ¼ in. hole saw
- Wood/plastic file
- Black cinder
- Baked or expanded clay pellets (Hydroton)
- Pea gravel
- River rock
- Expanded shale
- Lava rock
Make sure all the tubes, containers, and tubs that come into contact with the plants, water, or grow media are food grade certified. Avoid using standard PVC plumbing, as it tends to degrade over time when exposed to sunlight and hot or cold temperatures, and may not be food safe. Instead, use polyethylene hydroponic plumbing, CPVC, PEX, or copper tubing. The correct pipe thickness for most usages should be equal to schedule 40 PVC.
Do not use any containers with chemicals that will leach into the system. For the 55-galon drums, try food grade HDCP plastic barrels, either the blue or white ones. Some good tanks to use are called IBCs, or Intermediate/International Bulk Containers. You can usually buy them cheaply from online classifieds (e.g. Craigslist). If you want higher quality, but more expensive, IBC containers, contact a barrel/shipping tank recycler or distributor. They will usually have clean and refurbished used ones that sell for less than new ones. For your grow bed containers, they must be at least 8-inches deep, although 12-inches is optimal.
For a cheap and effective fish tank, try using an agricultural trough, which is long and has a low profile, making it good for vertical systems. If possible, don’t use a rectangular fish tank, as the corners could receive less circulation and become stagnant over time. A round fish tank is best, although it isn’t necessary. Just make sure the tank you use does not have hollow pockets, or any place where solid waste can accumulate, and that it holds at least 100 gallons. For every 1-pound of fish in the tank, there should be 5- to 10-gallons of water. If you consume 37 pounds of fish per year, for example, then you would need a 200 gallon tank.
The grow media used in the bed can be any of several kinds of various sized rocks, which are useful because they provide more surface area in which the beneficial bacteria grow. The more media you have, the more surface area there will be. Thus, more bacteria will be present, making the nitrification process take effect faster. The bacteria and microorganisms that make aquaponics possible should occur naturally in the grow media. To jump start this process, you can add an organic digester to introduce bacterial enzymes into your system.
Building the Frame
Plan to orient all your tanks and grow beds to utilize gravity feeding when transporting your water in order to minimize the work needed by your pumps. Aerate the water in the fish tank by using plumbing inlets or falling water from the siphon, by placing air stones underneath the water, or with a venturi device that injects air into a flowing water stream.
Start by using your jigsaw to cut your first barrel in half, going vertically from the top down. For ease, lay the barrel down horizontally and cut along the seam on one side, then flip it over on the other side and make the same cut again. Finally, stand it vertically, upside down, and cut through the bottom. This will split it in half, making two equal grow beds from one barrel. Mount these grow beds to a wooden frame, built approximately 70- by 27-inches, or long and deep enough to hold your intended grow beds. A frame this size will fit two of the half-barrel grow beds. Although, if you want a central beam for support, make your frame 71 ½-inches long instead of 70-inches.
After mounting the grow beds in the frame, you can put them together by drilling through their sides, or attach them to the central beam. Be sure to add a crossbeam for support so that the legs won’t wobble from the weight. Set the beds about 32-inches or higher off the ground to make them easy to work with. Attach the vertical frame underneath the grow beds, raising them up to make room for the tank. To erect the fish tank, take another barrel and put it upright. To make an access hole through the top, drill two holes into the lid to create notches on either side. Use these notches to cut a line through the middle of the lid with a jig saw, going around the portholes, dividing it in half. Then file down the cuts to soften up their edges.
After assembling the frame and installing the beds, you must choose where to place the Standpipe. The most common location used is either in the center of the bed, or opposite the inflow pipe on the side. If you place the standpipe in the center, there is potential for solid waste to build up. However, if you place the siphon on the side, opposite the inflow pipe, then the water will have to travel all the way across the bed to drain, bringing solid waste with it. This means there will be less clogging and fewer anaerobic spots.
Once you have chosen where you will place your siphon, find the bottom of the barrels by dropping a pen or a marble into them, and mark the spot where it comes to a rest. Drill a 1 ¾-inch hole at the point where you marked. File it down until clean, and slide in a 1-inch Uniseal or bulkhead fitting. If using a Uniseal, the pipe will make the seal expand and become watertight. If using a bulkhead fitting, place it through the grow bed so that the threaded (male) section is orientated upwards, while the receiving (female) fitting is coupled with it from below. With the bulkhead, you can generally use rubber washers on both the top and bottom, or you could use just one on the underside of the fitting, depending on the bulkhead.
Bell Siphon Drain System
Some crops (e.g. lettuce, watercress, etc.) can be grown with the roots constantly soaked in water and don’t need draining. However, most plants don’t like to be constantly wet and can become subject to root rot. To prevent this, use a media-flooding drain system to periodically remove the water. Other systems exist, but a flood-and-drain system utilizing a Bell Siphon is the most common method used in aquaponics systems because it is reliable, easy to make, and one of the simplest of all to operate.
Bell Siphons are useful because they regulate the flow of water automatically, draining water quickly and consistently. This eliminates the cost of using a timer, the risk of timer failure, the cost of electricity to run it, and the cost of maintenance on the pump. This quick drainage also pulls oxygen into your media, helping to aerate the grow beds. The disadvantage of this system is that it relies on a constant flow of water to trigger the siphon, which can be interrupted by insufficient or excessive flow rates from the pump.
A Bell Siphon consists of a central pipe, called the Standpipe, inserted vertically into the grow bed and set about 1- or 2-inches below the surface of the grow media. This determines the maximum water level in the grow bed. Sitting around the Standpipe is the Bell Siphon, a hollow, cylindrical pipe section with an opening on one end and an air tight cap on the other, creating a cavity of air inside it. At the open end of the Bell there should be a set of slits, notches, or teeth cut into the bottom, allowing water and air to pass through.
A Bell Siphon uses the same physical properties as a vacuum, creating an area of low pressure to push air and water through an opening by the outside atmosphere. Water is pumped into the grow bed and flows through the notches in the Bell, rising up and filling the chamber inside. When this water reaches the opening of the Standpipe it will start flowing down it at an increasing rate, and the rushing water will force the volume of air trapped in the central pipe out through the discharge leg. Water then seals the Standpipe as it closes in around the top.
The escaping air relieves the back pressure within the siphon, generating a partial vacuum, and causing the liquid inside to rush up and fill the siphon. At that point, no air can get inside the Bell, and a low pressure zone is created inside. Because the pressure from the outside air is greater than the pressure inside the Bell, water from the tank is pushed by the atmosphere through the notches at the bottom, generating the siphoning action. When the water level lowers and reaches the teeth in the Bell, air enters the chamber and releases the vacuum. This equalizes the pressure between the outside atmosphere and the chamber within the Bell, breaking the siphon and allowing water to refill the beds and restart the process.
How fast water flows into the grow beds will determine the duration of the cycling. In general, ebb-and-flow cycles should start and stop every 15–20 minutes, regardless of the size of the beds. The entire volume of water in your fish tank should also be recirculated at least once every hour, determining the minimum amount of water that will be entering the beds at any time. In a larger growbed of 500 liters, for example, approximately 200 liters of water will be emptied every cycle. With every cycle lasting about 15 minutes, this means that 800 liters will be cycled every hour. Your pump, fish tank, and plumbing need to be able to handle this capacity.
How to Make a Bell Siphon
The length and width of the Bell Siphon is determined by the depth of your grow beds, the size of your Standpipe, and how quickly you want the water to drain, but generally the dimensions should be as such.
- Pump capacity: 1100 L/hr–1800 L/hr (290.6 gallons/hr–475.5 gallons/hr)
- Gravel guard width: 110 mm
- Air tube width: 7 mm
- Standpipe width: 25 mm
- Funnel size: 40 to 25 mm adapter
- Bell width: 80 mm
- Horizontal outlet: 200–250 mm
- Vertical outlet: 200–250 mm
These measures are approximate, and the dimensions will vary depending on the size of your tanks, grow beds, and your intended water flow. The rule of thumb is that your main siphon components should be equal to or slightly greater than the water inflow components. The sizing for all elbows, threaded adapters, and other pipes not mentioned should be the same width as the Standpipe without the funnel, or, in this case, about 25 mm.
To create the Bell Siphon you need a large PVC pipe section, about 3- or 4-inches wide and 12- or 14-inches long, with a cap on the end and an open section on the other. The Bell Siphon should be sized according to your standpipe and grow beds. In terms of width, there needs to be enough room between the side of the Standpipe and the side of the Bell Siphon to allow water to flow smoothly and quickly. To achieve this, follow the 2:1 rule. That is, the width of the Bell Siphon should be about twice the width of the central shaft of the Standpipe. Likewise, the width of the gravel guard should be about twice the width of the bell siphon.
Prime and glue a PVC cap onto the end of the bell pipe. Next, cut the Bell Siphon to the appropriate length so that the cap on the Bell Siphon is level with the top of the Standpipe. On the open section, cut some slits or notches on the bottom, rising up about 1 ½-inches to allow water to flow through and rise on the inside of the siphon. They will also be a factor in establishing your water flow, and determining the minimum level of standing water in the grow beds. If you want a faster flow rate, then cut the notches a little higher up. For a slower water flow, then cut the notches lower. Don’t cut the notches too low, however, as this will make the Siphon ineffective.
Other things like the funnel, restrictions on the drain line, extra elbows and traps at the bottom, the breather tubes, etc. help to improve on the basic siphon function. Test the system without these additions first, and then add them on later, if needed. Inserting an air tube (or snorkel) to create a breather tube, into the top of your Bell Siphon can help regulate the flow of air when breaking the siphon. Like other design additions, this is optional, and the siphon can be made without it. If you add a U-trap to the drainage below the grow beds, then you will probably need the snorkel because the siphon will have difficulty sucking in enough air to stop properly.
To create a snorkel, use a drill bit or hole-saw with a diameter approximately the same size as your tubing or pipe, and drill a hole into the side of the bell cap. Cut the end of the tube at an angle to create a bevel that gives clearance from the Standpipe, allowing air to flow through. Next, push the tubing through the hole so that it extends about ¼-inch inside the bell. Do not insert the snorkel through the cylindrical section of the bell, as having it only go through the cap instead will allow for easier removal and maintenance, as the cap can be removed and replaced more easily. Seal the gap surrounding the tubing at the entrance to the bell with a bead of outdoor silicone adhesive, or an aquarium grade silicone caulk, and allow it to dry. It is important to create an airtight seal in the Bell, or else the siphon will not start properly.
After it dries, gently angle the tube downward, training it along the length of the bell, and secure it in place with a cable tie. Cut the free end of the snorkel at about ½-inch above the teeth, but do not cut it too low, as the siphon will not break properly. This creates an air break so that air has a chance to enter the bell before it needs to go through the notches on the bottom. An alternative approach to the design is to drill a threaded hole in the cap and screw a 90-degree plastic hose barb fitting into place. This way, the snorkel can extend directly down along the bell pipe toward the teeth without having to make a sharp turn with the tube, bending and weakening it.
In large beds, the water level will lower more slowly as it drains. This could be a problem, as air may not get through the snorkel quickly enough. If this happens, the siphon could cut off, and the water in the chamber will become static and trickle out at the same rate the bed is filling. To solve this, place a little cup over the breather tube, just big enough to cover it all around, going up about 1-inch over the end. To make a cup to cover the end of the air pipe, you can use any piece of plastic that will fit over the end of the snorkel. A simple pill bottle will work fine. Or, you can cut a piece of vinyl hose with a band saw and stick a dowel rod in the end to seal it.
Attach the cup to the outside of the bell with a zip-tie or metal twine, and then insert the end of the snorkel into the cup, letting it dangle inside. Or, you can let the cup hang loosely over the end of the snorkel so it can rise and fall freely. The cup allows the snorkel to suck up enough air to break the siphon without water blocking the passage and slowing down the siphoning action. This way, as the water rises, the cup gets filled with water and enters the breather tube as normal. Then, as the water level lowers, the water will quickly get sucked out of the cup by the siphon. Since the cup is empty and surrounds the end of the breather tube, the tube will suck out all the water in the cup, and then bring in pure air, making for a clean break of the siphon.
Making the Standpipe
The Standpipe is a smaller sized PVC pipe section that goes down through the bulkhead of the grow bed, attached via a rubber o-ring, and leading to a drain which deposits the water back into the fish or sump tank. The appropriate size of the Bell Siphon and Standpipe depend on the size of the grow bed. The larger the grow bed, the more water it holds, and the larger the Standpipe and Bell Siphon that will be needed to drain it.
The diameter of the Standpipe should be about half that of the Bell Siphon. The height determines the maximum fill level of the water in your grow beds. If your grow beds are 12-inches deep, then the opening of the Standpipe should be about 2-inches below the media so that the top surface remains dry. Therefore, the total height of your standpipe – from the bottom of the grow bed to the top of the opening – should be about 10-inches. The top of the Standpipe should also be level with the bottom edge of the cap on the Bell. This is important in ensuring that the volume of air in the top of the Bell is sufficient to start the siphon.
Bell Siphons work best when the Standpipe has a funnel, or accelerator, at the top, which usually comes in the form of a screw- or slip-on attachment or adapter. The funnel adapter provides a convergence point that creates a water avalanche into the Standpipe, helping to make the siphon work more effectively. You can achieve a funnel shape for the Standpipe by taking a piece of plastic of PVC and heating one end of it with a 1500 watt heating gun. When the piece is sufficiently warmed, press it down over a cone shaped object to stretch the end out and open. For best results, keep the heat gun a few inches away from the pipe as you work it. Don’t hold the gun too close, as you could burn and ruin the pipe. You could also use a torch, but be aware, as the flame burns PVC easily.
You could also use a PVC reducer, which can simply be attached to the end of the Standpipe, and acts as a funnel. In this case, the reducer is 40 mm at the top lip and reduces to fix to the 25 mm pipe. Try experimenting with different sized adapters to adjust the efficiency of the water flow. If using a reducer, then the height of the shaft of the Standpipe will have to be cut down to compensate so that, with 12-inch beds, the height of the Standpipe from the top of the reducer to the bulkhead is a total of 10-inches.
Also, to prevent the inside of the Bell from getting waterlogged, you can optionally drill a small, 4 mm wide hole at the base of the Standpipe, about 1 ½-inches up from the bottom of the bulkhead. This drip-hole will very slowly empty the Bell if the pump is ever stopped.
Making the Gravel Guard
Before adding the support medium, you should construct a Gravel Guard to separate the siphon from the grow media. This can be any porous material shaped into a tube, like a metal mesh screen. You could also use a chop saw or drill to cut holes or slits cut evenly along the length of a wide PVC pipe. This allows water to seep through, keeping sediments from entering the siphon, while also allowing you easy access for maintenance. To prevent your grow media from getting into the Siphon, the holes in your Gravel Guard should be smaller than the average size of the individual pebbles in the beds. You don’t need the Gravel Guard to have any holes or slits in it above the bottom half portion of it, as it will weaken the structure unnecessarily.
A typical Gravel Guard is about 3- to 4-inches wide, or approximately twice the diameter of the Bell Siphon, so that it can easily be removed during normal operation and maintenance. However, if you are using a snorkel, then the Standpipe should be placed a little off-center to allow for extra room to fit the Guard. Gravel Guards should also be slightly longer than the Bell Siphon so that they are able to keep out particles of the support medium that surrounds the drain assembly. To weigh down the Bell Siphon in case it floats, and to keep out mosquitoes, cover it by placing a Dixie cup over the Guard on top of the Bell, and then weigh it down with a rock inside the cup. You can also place a plastic atrium cap on top of the Guard to cover the Bell.
Assembling the Standpipe and Drainage
The drainage area under the grow bed is important to get correctly because it will help to regulate the siphon and influence how it starts and stops. There are a number of variations on the outflow fittings that you can use. Some of these will depend on how high your grow bed is above the fish tank, whether you want the siphon to run quietly, and whether you want it to help aerate your fish tank. The basic configuration is as follows:
- A straight pipe of varying lengths (determines whether there is enough back pressure to start and stop the siphon)
- A pipe with one or two 45 or 90 degree elbows to provide back pressure and aerate the water.
- A pipe with a restrictor or an aerator nozzle.
In order to start and stop the siphon, it requires a build up of pressure to expel the air inside. However, if the water flow is too slow, or if the pipes are too big, then it will not be able to build up enough back pressure to start the siphon, and water will simply trickle down the opening of the Standpipe when it gets to the top. Similarly, if there is too much pressure because the water flow is too fast, the pipes are too small, or there is not enough of a restriction on the downspout, then it may not be able to suck in enough air to stop correctly. So, finding the correct balance is necessary to regulate the siphon.
Start by inserting the Standpipe through the Uniseal or bulkhead, tapping it through with a hammer. To make the pipes easier to push through the Uniseal, try filing the ends of the pipe to smooth them out. The Standpipe shouldn’t be glued into the Bulkhead fitting. Instead,
slide it in loosely so that it can be changed. Adjust the height of the Standpipe to set the desired maximum fill level. When making the Standpipe, ensure it will sit about 1 ½- to 2-inches below the surface of the gravel so that standing water never emerges at the top. Attach the pipe to the bulkhead of the barrel using a silicone glue or caulk, and then begin connecting the PVC pipes underneath. When assembling the drainpipes, use a Teflon adhesive (or other glue used for water pipes) to bind them together, twisting the pieces about 90-degrees as you insert them to ensure a tight and uniform seal.
One common modification to the drainage area is to add a series of elbow underneath the beds, to create a U-shaped joint. This creates a slight restriction on the outflow, helping to start the siphon. This will usually be necessary when using large or multiple grow beds, or when using a snorkel on the Bell Siphon. A straight down pipe with a restrictor will do the same thing. On the bottom of the Standpipe, attach a 90-degree PVC elbow to divert the water horizontally. It’s important to have each elbow level with each other, or be set slightly lower on the downstream end to ensure that air can flow up the pipe to break the siphon.
Start by dry-fitting your connections, making sure they’re snug, and do a test fit with your outflow pipe to see how long it needs to be to hang over the fish tank. After making the correct measurements, cut the pipe and attach another 90-degree elbow on the end, facing it directly downward to guide the water flow directly into the tank. Do the same with your other pipes so they meet just over the fish tank. A short “nipple” (small piece of straight pipe) added to the open end of this elbow is helpful in directing the water. It will also increase the speed of the flushing stream. If you want the water coming from the siphon to swirl in the tank, then add a 45-degree angle to the outflow pipe and point it towards the edge of the tank. If not, then simply add a straight piece of pipe, about 12-inches long, to the bottom of the bulkhead fitting.
If you have only a single horizontal bend in your drainage, it will require a faster water flow to create the turbulence that generates the siphon. In larger grow beds, this will put unnecessary stress on the pump, which has to work overtime to maintain a fast flow rate. In this case, you will need to add a U-trap at the bottom of the drain assembly to restrict the water flow, and slow its rate of drainage, to increase the back pressure in the drainage system, and assist the Bell Siphon in starting and stopping the siphon. Use two elbows put together beneath the Standpipe to create a 90-degree turn, and another to drain the water off horizontally.
As the grow beds fill with water, this pushes the water up in the Bell, climbing the Standpipe. As the water fills up, pressure builds inside the Bell Chamber and the cap area. When the water reaches the rim of the Standpipe, the pressure forces the water down and out the bottom.
The water falls down the opening, draining out of the Bell as the Siphon draws it out of the beds. When the beds are sufficiently empty, air enters the Bell and is sucked up and down the Standpipe. The pressure pushes the last of the water in the trap down, but it also pushes the air out as well, burping a few bubbles out the other end. When this happens, it reduces the internal pressure inside of the bell area and the trap, causing the water level inside the bell to rise as it draws water through the notches in the Bell and the snorkel, starting the siphon.
As the water level lowers and reaches the teeth in the Bell, the final burp will overflow the top and send down a rush of water, followed by some burps and bubbles as the last of the air is pushed out with it, evacuating all of the air from the Bell. This rushing air and water should generate a pressure that follows in their wake, bringing more air and water out with it until one of the two is exhausted. The water in the bell is evacuated, and air enters the bell to break the siphon.
Now insert your pump in the fish tank, and attach a ½- by ¾-inch male PVC adapter to the pump, screwing it on tightly. This will allow you to run your PVC pipe straight up, pumping the water to the top. Put a PVC T on the top of the pipe leading up from the pump, and use this to attach further pipes that deposit the water in the grow beds. Simply attach some more 90-degree elbows or plumbing taps at the ends of these pipes to control the flow rate and the direction of water into the beds.
Place the Bell over the Standpipe, and then put the Gravel Guard over it to ensure everything fits. Thoroughly rinse your grow media and add it to the grow beds, carefully placing the medium around the base of the Gravel Guard so as not to disturb it. Once a firm base of medium has been added, continue filling the rest of the bed to a height about 1- to 2-inches higher than the top of the Bell, but do not surpass the height of the Guard.
Having a U- or J-bend as a trap in the drainage may be troublesome as it could cause the water level to rise too high in the beds before it drains. If this occurs, try going back to a normal downspout design without the U-trap, and with a single 90-degree elbow on the end of the standpipe, going horizontally in either direction. Your drain should also be at least 12-inches long, with an elbow, but 24-inches is better. The drain coming from underneath also needs to be larger than your water intake. The bigger your beds, the bigger your drain.
In a typical system, water is pumped up from the fish tank into the grow beds, and the siphons in the beds send the water back to the fish tank, restarting the cycle. However, this constant emptying of water from the fish’s habitat, with the interspersed drainage of the beds, can make the water levels in the fish tank vary considerably, disturbing the fish. Adding a sump tank to the system can help reduce the sudden change of water levels in the fish tank.
The sump tank is a water holding container that receives excess water after being drained from the grow beds, helping to keep water levels stable. In a simple system, water drains directly from the beds into the fish tank. However, we sometimes need to use a sump tank in the event that water cannot drain directly to the main fish tank. In this case, the water is interrupted and captured into an intermediary vessel, called the sump, in between the fish tank and the grow beds. The water is then put back into the fish tank via a pump or by a gravity-fed overflow barrier. If using a sump tank with a pump, use the pump to move water up from the tank to the grow beds or into the fish tank.
The water is then siphoned out via a pump or gravity into the fish tank, which overflows and gravity feeds water back into the grow beds or the sump. This way, the water level in the fish tank should stay at a more or less constant height, as any new water that is deposited can only come as fast as the pipe sizes will allow. Typically, grow beds are built at the highest point in the system, with the fish tank being placed one level lower, while the sump is placed at the lowest position in the system, below the tank, with a pump taking the water out of the sump, going up a pipe system, and depositing it back into the grow beds.
However, the nature of the terrain, the environment, your supplies, and personal preferences may influence the relative placement of the tanks and beds in the system. Your site will determine what system design you use. On a sloping site, for instance, you would naturally have the sump on the bottom and the fish tank at the top to flow into the grow beds, set at the mid-level. In turn, the grow beds would flow to the sump below, and then get pumped back up to the fish tank. The grow beds can be placed at the highest point, or at mid-level, but should not be placed on the bottom, as it relies on gravity feeding to be able to empty the beds.
If you have the ability, try to bury the sump tank in the ground to maximize your potential growing space. On hard surfaces you may not be able to set a sump or fish tank into the ground. You would then use a fish tank lower than your grow beds so they can flow straight to the fish tank, which then brings it back to the grow beds.
If the height of the top of your fish tank is higher than the bottom of your grow beds, then the beds could drain to a separate tank before the water is sent back to the fish tank. This separate tank would be your sump tank. But if you plan your system so that the height of the top your fish tank is lower than your grow beds, and the grow beds are above the fish tank, being able to take advantage of gravity, then a sump tank may be unnecessary. You can skip the addition of a sump if the water volume in your fish tank is greater than or equal to the total volume of your grow beds without the media. So long as you have enough water for the fish, while the system is fully flooded, then the sump tank is not necessary.
Despite these restrictions and exceptions, there are still benefits to having a sump tank. For example, if you ever need to do some maintenance on a constant flood system, you can use the sump tank for holding the water, rather than using buckets or flushing the water to drain and wasting it. Another benefit of a sump tank is that it can be utilized for the rearing of additional organisms, like fingerlings, crustaceans, or mollusks. Crustaceans are useful because they provide a food source (for humans or the fish), they consume less food, and produce less waste than fish. Fish prefer an environment that maintains a constant volume of water. Crawdads, however, may do well in a sump tank because they can tolerate rapidly changing water levels better than fish. They are also fond of eating small fish, or may be eaten by the larger ones, so mixing them with the fish isn’t a good idea. You can keep these animals in a separate tank away from your main fish tank to keep them safe from predation, or you can grow smaller fish that you intend to transfer to the fish tank when they grow large enough.
Also, adding a sump tank will be useful when you decide to expand your grow beds. Without a sump tank, your grow beds may take up too much water, leaving too little for your fish. You need to calculate how much water the grow beds will hold, in comparison to the water held in the fish tank, to determine whether you will need a sump tank. On average, your grow media will displace about 60% of the water from the grow bed, meaning that in a 100-gallon grow bed, 60-gallons of that volume will be grow media, and 40-gallons will be water. If you add another 100-gallon grow bed, then this means another 40-gallons will be pumped out of your fish tank. Assuming your tank is the same size as a single grow bed, this means 80-gallons will be pumped out of the tank every cycle, leaving only 20 for your fish. In this case, you would need a sump tank.
To find the necessary size of the sump tank, simply add the total water volume of your grow beds, then subtract the displacement effect of the grow media. You also need to calculate the minimum amount of water that must remain in the sump tank to keep the pump submerged and ensure that it does not run dry. This usually requires a minimum water level of about 3-inches, but it differs from pump to pump. This volume should be added to the grow bed water volume calculation above, giving you the minimum total volume needed for your sump tank. In general, any sump you use should be at least 50% the volume of your grow beds.
An easy container to use for a sump tank is the same 55-gallon drum you used as your fish tank. It’s convenient to use, also, since you can buy several of them at once. And because they’re all the same size, the system is easy to expand and scale up, piece-by-piece, and it makes your calculations all that much easier to determine. Lay it down horizontally to give yourself more vertical space so that you can lower the grow beds down to about waist level. This will give you more grow space for taller plants, and allow you easier access to the grow beds. To create a receiver for the drainpipe, cut a hole in the top of the barrel, and feed a 2-inch wide PVC pipe through it. To secure it to the lid, put a threaded 2-inch adapter inside, and use this to attach the pipe to the lid. Simply thread it right through to create an easy receiver for the drain pipe.
In a conventional aquaponics system, your grow beds will act as an initial filter. However, you will eventually accumulate solid waste (fish poop, floating debris, and food particles) that ends up in your grow beds and stays in your fish tank. When this occurs, you can either add another grow bed, which will help only for a short time until more grow beds are needed. Or, instead, you could install a filter to clarify the water. To remove this waste, you will need a filter which receives the water as it moves from the sump or fish tank and into the grow beds, or vice-versa. If you want, you can design the system to make the filter serve as the sump tank if the filter container is large enough.
There are many other reasons and benefits for using filters. Keeping your water clean improves fish health, prevents the plants’ roots from getting clogged, and aids in their ability to absorb oxygen and dissolved nutrients. They also naturally filter the water without using harmful chemicals or energy consuming machines, while also making the system run for longer without needing to clean it manually. There are at least three different kinds of filters you can use: a radial filter, a swirl filter, and a bio-filter, either of which can be combined with another to create a hybrid filter. You can also chain together individual filters to combine their advantages into one system.
Regardless of the system you use, you’ll need to find a good container. For an average sized home system, a 200 liter blue barrel should work well. You can also repurpose an old, heavy-duty plastic trashcan, or another similar container. The size you need depends on the size of your fish tank. For best results, sit the filters on heavy duty hardwood stands, and set them about 1-meter off the ground.
As an alternative to independent container-filters, simply attach a nylon stocking over the water spouts leading to the grow beds and tie a rubber band around the ends to seal them. This will lie on the surface of the grow media, and fill with water like a balloon, leaking out filtered water. You can also put a simple sponge-like screen, or any aquarium mesh with a high surface area, under the flow pipe that deposits the water into the grow bed to filter out solid waste. If you want, you can attach a basket filter or kitchen sieve under the spout to catch the water as it falls, separating out large particles automatically. You can also construct a Radial or Swirl Filter by repurposing an old 5-gallon water jug. Attach a pipe to the funnel-shaped spout, securing it with rubber tubing and metal ties to create a water-tight seal, and put a tap on the end of the pipe. Use this to design an inflow and outflow system from PVC pipes, arranged through the sides or the top and bottom of the jug.
Tools and Supplies
40 mm pipes
40 mm Uniseal
64 mm hole saw to fit the Uniseal
29 mm hole saw for the tap
Drill for solids lifting overflow
Drop down saw
Radial Flow Filter
A Radial Flow Filter is used to filter solids from your aquaponics system without using expensive commercial varieties. They are highly efficient (even more efficient than a conventional Swirl Filter), and will remove up to 48% of suspended solids.
These filters work by moving water in a gentle manner and changing the direction of the flow so that the suspended solids will fall out and settle to the bottom, taking clean water off the top. First, water enters the system, usually via a pipe coming in through the center and opening at the bottom, although it could also come through the side. This pipe leads to a corner made from two 45-degree elbow fittings, joined together to make a rounded 90-degree turn. This is done because when water hits a sharp 90-degree bend, it slows the flow of the water and weakens the circulation. A rounded turn allows the water to track up more smoothly. If water flow turns out to not be a problem, you can use the 90-degree elbow, instead.
Fish effluent-holding water travels vertically through this pipe, where it enters the opening of another container, inside the main chamber, mounted to the lid upside down. This is called the hood or settlement shroud. Depending on the size of your filter container, some suitable containers could be a 5-gallon bucket or a cutoff white tank. A 150 mm stormwater pipe, or a 150–200 mm plastic flower pot, will also do in most cases. At a minimum, the hood should be large enough for you to be able to reach down with your hand, and move it around, unimpeded for maintenance.
When the water leaves the pipe, it is pushed up by the movement of the water behind it and becomes trapped inside the shroud. It then hits the sides of this shroud, and is redirected downward. The low-density solids settle out of the water column and sink and accumulate on the bottom. Filtered water fills the tank until it overflows a barrier, or reaches a 40 mm pipe at the top of the container. The clean water is then gravity-fed down into the sump tank, grow beds, or fish tank.
Cover your filter with a lid to keep out animals and debris. Attach the settlement shroud on the underside of this lid so that it hangs upside down in the water. Center the shroud in the lid, and bolt it directly on with some stainless steel supports or timber rods to keep it level and in place. You can also build the system so that water and solid waste come in through the top, inside of the hood, instead of through a separate pipe on the bottom. This way, water gently moves down under the rim of the upside down container and rises up to exit near the top, outside of the cylinder, leaving the solids behind. Place a tap at the bottom of the filter for easy waste removal, which you can use as fertilizer for your soil-grown plants or as food for compost worms.
Over time, hydrogen sulfide can build up in the solids that collect at the bottom of the filter. If left there, the water will stagnate and poison the fish. If you don’t have a tap on the bottom to remove the solids, then this could become a problem. Either drill holes in the lid for ventilation, or let the lid sit loosely on top of the filter. To prevent mosquitoes from getting in side the lid through the breather holes in the lid, simply cover it with a green mesh or agricultural sheet.
A Swirl Filter is similar to a Radial Filter, and can be built with the same materials. It consists of a bucket, trashcan, or tub with an inlet pipe mounted through the side, about 1/3 of the way from the bottom, and an outlet pipe on the other end. The inlet could also be designed to come through the top, if you wish. To build the filter, drill two holes in the side of the filter container equal to the width of the PVC drainage pipe, or large enough to fit the pipes through a Uniseal or bulkhead fitting. A ¾ inch pipe will suffice, although you can use the same dimensions as the Radial Filter.
Wherever you place the inlet pipe, the opening where the water enters the system should be at a lower level than the opening of the outlet pipe, where water exits the system. You can insert the pipe into the side of the container near the bottom, entering horizontally through the side, or you can choose to insert the pipe going vertically, down through the center from the top, with the water exiting out the pipe at the bottom.
If your water enters the filter through a central pillar in the middle, going down towards the bottom from the top, then attach a plastic T at the end of the inlet pipe, with some short extensions pointing out to the sides. Attach a 90-degree elbow, or two 45-degree ones, to the ends of the pipes and orient the spouts to face out to the sides in opposite directions. This should create a slow, swirling vortex in the barrel. Be sure to angle the elbows slightly downward to get the right swirling action. This way, water is ejected out of the spray pipes and given a rotational momentum. As the water swirls around and fills the tank, the whirlpool generates a centrifugal force that changes the pressure of the water on the outside, making it higher than in the center. This pressure moves solids to the outside walls, which then sink to the bottom.
This means that the water at the top, closest to the center, will be the cleanest. At this location should be placed the opening of the out-flow pipe, which comes through the side of the trashcan, extending into the center of the tank. Put another 90-degree elbow on the end of this pipe, with an attached funnel reducer, and angle it upwards so that the open edge is level with the fill line. This funnel will catch the cleanest water at the surface, which falls through the outlet where it is gravity-fed to another tank. You can also add a tap at the bottom to remove the solids.
If possible, you can replace the main container’s base with a conical one, like a large funnel, to capture and direct the solids down to the drain. Attaching the funnel to the bucket might be a challenge, and may need some plastic welding or silicone to hold it together. Using this funnel design, you can make a hydrocyclone filter, which takes advantage of the centripetal force of fluid motion to separate and sort particles from the water.
In a hydrocyclone filter, water enters the system from the top and gets fed tangentially to the side, spinning around and creating a downward, spiraling vortex. The liquid resists the inertia of the matter spinning within it, slowing it down as it swirls around, and transports larger and denser particles to the wall, depositing them in a collection trough at the bottom. Inside the center of the chamber is a cylindrical section, extending down into the body of the cyclone. Finer and less dense particles remain suspended in the liquid and rise in this central tube, where clean water is skimmed off from the top.
You could also experiment with an outlet pipe attached to the funnel, along with a suitable tap fitting, to direct fish waste out from the system. Instead, you could figure out a way to direct all those wonderful nutrients to another tank or growing system, separate from the aquaponics system. Or, you could divert it to a patch of soil-grown plants, or create a wicking bed to grow root crops. Instead of a tap, you could also set up your system to drain the water using an auto-siphon like that used in the grow beds.
Biological filters utilize microorganisms to clean the water without using fluid motion, chemicals, or contact filtration to separate particles of matter. Instead, naturally living organisms consume the waste and help filter the water. Bio-filters are useful because they clean out very fine particles not caught by other means, and they can also be combined with other systems.
For example, you can combine a Swirl Filter with a Bio-Filter to create a Hybrid Swirl Filter, which utilizes solid filters that come into contact with the water to clean it. Simply take a plastic laundry basket and drill some holes into the bottom, if needed. Then secure it inside of the filter container or barrel, so that it is suspended in the middle, or at the top third, depending on the size of the basket. Just make sure the basket fits easily inside the container, and that there is enough room between it and the sides so that water can freely move around. Then, line the inner walls of the basket with nylon scouring sponges, or specialty aquaponics foam filters. Lighter suspended solids will be trapped by the foam in the basket and clean the water that passes through.
The sponges house little creatures called Gammarus, which is a genus of small, shrimp-like crustaceans that should occur naturally in the filter. They eat particles of poop and help clean the water, turning it into nutrients for the plants. They also eat mosquito larvae, preventing pest invasion. As water fills up the container, water will make more and more contact with the filter media containing these micro-organisms (which eat the smallest particles left behind by the other filters), cleaning the water until it reaches the top.
For additional filtration, place a laundry bag full of natural coral inside this basket, at the base. You can also fill the basket with aquarium filter toilet brushes to help clean the water. Make sure the sponges and filter material have not been treated with any antimicrobial substances or harmful chemicals. For best results, try buying untreated sponges from an aquaponics store.
As another filter, you can take a separate space, similar to a grow bed, and convert it into a bio-filter by filling it with coral material on the bottom, covered by some rocks on the top. This will provide a living space for beneficial microbes and organisms, like bacteria, crustacean-like creatures, compost worms, etc. These worms grow in the bed and digest organic matter in the water, mineralizing the fish waste, and removing toxins and particulates. In addition to this, they also produce castings which will benefit the microbes that live in symbiotic relationship with the plant roots. The Gammarus are also beneficial for the worms because, when the Gammarus shed their shells or die, their exoskeletons become a food source rich in chitin for the worms.
Another filter utilizes a bucket filled with trays containing different materials, through which the water passes and gets filtered. To create this, take any large- or medium-sized container, like a plastic bucket, and insert a tube straight down vertically into the center. This is the water inlet, which ejects water out at the bottom. The water fills the buckets and passes through a series of trays or upside down lids, which contain large and small gravel, bio-balls, filter mats, and other filtering materials. The water travels up through these layers until it reaches the top, where it overflows and skims off the clean water at the top.
You could also create an independent biofilter consisting of a bucket or barrel filled with onion bags. The bags are made from a soft, elastic fabric that works great as a filtering material, trapping sediments as water seeps through them. Microscopic organisms will also take up residence in the onion bags and help filter the water. You can fill the bags with aquaponics filter balls, or just leave them empty, and put them inside a barrel until full.
Planting and Watering
Start the plants from seed in some dedicated starter beds, with each plant germinating in their own individual container, before you plant them in the normal gravel-filled grow beds. This minimizes transplant shock that could occur when moving the plants to the grow beds.
If growing indoors during the summer, try using a de-humidifier in the room to remove some of the water from the air to reduce mildew. If you place your grow beds up against a wall, put your taller plants in the back, closer to the wall, so you don’t have to reach too far when gathering or pruning.
When watering, you will have to pay attention to things like the pH levels, ammonia content, mineral content, water temperature, hardness, additional nutrients not provided by the fish, etc. If you are using water that is too “hard”, you can use a filtration system to filter out any impurities. If you use pure, filtered water, this eliminates some of the variables that can interfere with your system. For best results, use pure rain water.
To test the pH of the rock you want to use in the bedding, put it in a bowl with some vinegar and see if it causes a reaction. If it makes a very small reaction, or if there are just a few bubbles over the course of about 20 minutes, then it should be fine. If it fizzes a lot very quickly, then that means you probably have a pH problem. Change out the rocks for new ones to lower the pH. Be sure to wash off the grow media prior to putting it in your beds.
Try to keep the water going into your grow beds at about 70-72 degrees Fahrenheit. Depending on the species of your fish, the temperature in the fish tank should be in the high 60s or low 70s. Tilapias can be maintained pretty easily, but require water that is about 80 degrees. Catfish are safe to use as they can tolerate cold or warm temperatures, clear or muddy water. Tilapias are also good if your water never gets too cold. White and Blue Tilapia can handle the coldest temperatures. When first starting the system, start with Goldfish for about a year to get your system completely dialed in before you start growing larger species. After then, you can grow almost any kind of fish. Some other suitable species for an aquaponics system include Carp, Barramundi, Jade Perch, and Silver Perch. When feeding the fish, use organic food that does not have any harmful chemicals, hormones, or antibiotics.
It is a general rule among horticulturalists that fish produce only about 10 of the 13 kinds of vitamins, minerals, and nutrients that the plants need to thrive, depending on the species. This may mean that, over time, your plants may lose some of their vitality in the deteriorating conditions of the water as it loses its nutrients. However, there are ways to introduce more of these into your aquaponics system to ensure your plants get everything they need to operate at peak performance. Adding Rockdust, Sea Solids, Ocean Grown, Ocean Solution, or SEA-90 in the water will add 70+ different trace minerals and nutrients which may be lacking from the fish food. To add calcium to the water, and to help balance the pH, suspend a bag of oyster shells in the water. Also consider adding Iron Chelate to keep your foliage green and healthy. Do not add any harmful chemicals, pesticides, or sprays, as you are likely to disrupt the balance of the bacteria in the water and crash the natural system that cycles the nutrients. If you have to spray with chemicals, use the least toxic organic controls that you can find, such as Neem oil, Dr. Bronner’s magic soaps, or diatomaceous earth.
If growing outdoors, it would be a good idea to build some hoop houses over your grow and propagation areas to keep out pests and control the environment. It will also prevent you from needing to use chemicals to control pests. You can make some by sticking rebar in the ground and building a frame out of wire hoops or 1-inch PVC piping. Use covers made from a tight mesh fabric or shade cloth and attach them to the frame with clips. You can construct the same hoop house for any raised beds that you have.
- Soy beans
- Poll beans
- Passion fruit
- Iceberg lettuce
- Perilla (shiso)
- Water spinach (Ong Choy)
- Malabar spinach
- Collard greens
- Swiss chard
- Common sage
Siphon never starts or just trickles:
- Make sure the Standpipe is level.
- Ensure that no gravel has gotten lodged underneath or anywhere in the Bell Siphon.
- Check the seal around the snorkel or the Bell Pipe.
- There may not be enough back-pressure in the system to expel the air. Increase water flow into the growbed to force the air out of the Bell Siphon.
- Add a restrictor or reducer to the end of the outflow pipe, or add a 90- or 45-degree elbow under the growbed.
- Your siphon may be too big for the amount of water flowing into the beds. Downsize your siphon or increase the size of your growbeds.
- The drainage system below the grow beds should be level, or with only a slight downward angle.
Water inflow is not fast enough, or outflow is too fast:
- Adjust the brake to reduce the water drain speed (with a longer sharper turn, or add an elbow, etc.), increase water flow, or increase the size of the accelerator (the funnel) to make a clean siphon start.
- Your pump may have gotten clogged or dirty, slowing down the water flow. Simply clean out your pump or remove any obstructions.
Bell height over Standpipe might be too high:
- See if gravel or grow media has lifted the bell. You might benefit from placing a large stone on top of your cap to keep it down.
Siphon starts, but then trickles, or never truly shuts off; water level in grow bed is too low:
- You may have too much water input and not enough drain. Try to reduce the water inflow, or increase the drain size.
- Check that all the parts of your siphon are air-tight.
- Try to reduce the accelerator or water inflow size.
- The notches on the bell might be too low.
- The Bell width is too small.
- Check the Bell Siphon for obstructions.
- Your snorkel may be too low, not providing enough air injection to break the siphon.
- In large beds, the water level might drop too slowly to suck up air and break the suction. Add a cup over the snorkel.
- Remove an elbow from the drainage or shorten the brake.
- Increase the height between the top of the Standpipe and the top of the Bell Siphon.
- Try sizing up the diameter or length of your drainage pipes.
- Add a snorkel, or the snorkel you have might be jammed or too small.
Siphon never fully drains system:
- There could be too much brake, or the water input is too fast. Shorten the brake or angle it down so the water flows out faster.
- Reduce the 90-degree elbows, and use two 45-degree ones instead, or remove the elbows completely.
- Inspect your Bell Siphon at least weekly for slime build up, accumulating solid waste, rocks or pebbles jamming up the system, or root growth.