DIY Aquaponics - How does an Aquaponics System Work?

An aquaponics system is really quite simple. You have a fish tank and a growbed. The water from the fish tank is pumped through the growbed to filter it and remove the fish waste. There are many different approaches to aquaponics but on this site we are going to concentrate on what we consider to be the two simplest and most efficient methods. As our focus is on do it yourself aquaponics understanding the basic principles of our two chosen methods is preferable so that you can use and adapt available materials to construct your system.

Using an Autosyphon Flood and Drain System

A flood and drain style aquaponics system with an autosyphon seems to be the standard with home aquaponics users at the moment. An autosyphon is a handy little gizmo that automatically syphons the water out of the growbed when it reaches a certain level. They can be purchased from aquaponics suppliers or easily constructed if your prefer that real DIY approach. They are quite simple in design and can be made from pvc pipe and fittings purchased at your local hardware store. Our autosyphon system comprises of a fish tank (blue) and growbed (brown). The growbed is positioned so that it is higher than the fish tank so that gravity will allow the syphon to work correctly and return the water to the tank.

An aquarium pump runs continuously pumping the water from the fish tank into the growbed as seen on drawing 1.

In drawing 2 we can see that the water level in the growbed has risen until the autosyphon is completely submerged and the syphon itself has filled to the point that water has travelled up the outer sleeve and is now returning to the fish tank via the pipe inside the chamber. The water flows faster as the water level rises and expels the air in the autosyphon, creating the syphoning effect that is required. The water begins to flow freely back into the fish tank faster than the pump can pump the water into the growbed.

In drawing 3 we can see the water level in the growbed starting to drop as the syphon continues to flow despite the pumps efforts to keep up.

Drawing 4 shows the growbed empty, the syphon effect has been broken as soon as air enters the autosyphon and water is no longer present to be drawn back into the tank. With no syphoning effect the pump can now keep up again and the cycle begins again. Depending on the size of your pump, growbed and autosyphon this process may take 10-20 minutes. The aquarium pump is usually run 24 hours a day so the cycle of flooding and aeration is continuous and offers the optimum growing conditions for most plants.

Using a Traditional Flood and Drain System

We call this a traditional flood and drain aquaponics system because this method has been used successfully in hydroponics for a very long time. As with an autosyphon system the growbed (brown) is higher than the fish tank (blue) to allow the water to drain back into the fish tank. The aquarium pump does not operate full time but is controlled by a timer set to operate the pump for 15 minutes every hour.

As we can see in drawing 1 the cycle starts with the pump switched off. The growbed is aerating as plant roots need oxygen too and generally the system will be in this state about 75 percent of the time. Many aquaponics enthusiasts also like to program their timer so that the growbed is not flooded at all at night. Flooding the growbed at night is certainly not harmfull however some gardeners believe that not flooding at night accommodates the plants night time needs more.

Drawing 2 shows the beginning of the flood cycle, the timer has switched the pump on and water is now being pumped through the feed pipe and filling the growbed.

Drawing 3 shows the growbed completely filled with water from the fish tank. The pump is still running and forcing more water into the growbed. The excess water is now returning to the fish tank via the return pipe. The water is forced through the gravel or medium in the growbed and is being filtered in a fashion before returning to the tank.

In drawing 4 we see the end of the flood cycle. The timer has switched the pump off and the water is draining back through the feed line and pump back into the fish tank. It is very important that a non-return valve is not placed on the feed line or the water will be stuck in the growbed unable to return to the fish tank. Once the water has drained back completely the growbed has returned to aerating as described for drawing one and the cycle has commenced again.

So we can see that both methods of flood and drain accommodate your vegetables need to have a cycle of flooding and aeration to grow at their best. Growth rates in a well established and effectively run aquaponics system can be astounding at times but bear in mind when you start your system off it will be perhaps a little slower until your fish are at a size to provide an adequate supply of poop and your growbed has become established.