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          Backyard Aquaponics

Aquaponics is a great hobby or way to grow your own food in your own backyard. With a small backyard aquaponic system, you can grow enough food to feed your entire family. Many people contact us at Aquaponic Solutions about designing, building and running backyard and hobby scale systems. Therefore, we have decided to dedicate this page to providing information on all these aspects of backyard systems.

System Design

Aquaponic Solutions has advised many people on their backyard aquaponic systems, and the following are some of the main things we have seen people do wrong or completely avoid. Backyard aquaponic systems should encapsulate several design principles to be efficient and effective:

  • One pump only - for energy efficiency
  • Gravel bed hydroponic components - easy and efficient plant growth, solids filtration and biofiltration in the one unit
  • Constant Flow or Ebb & Flow water delivery to the hydroponic component
  • The preparedness to heat the system water in colder months
  • The use of the correct gravel type in the hydroponic component
  • A requirement to test the water on a regular basis

One Pump

There are many plans for backyard aquaponic systems available on the internet. Some are good, some are not. The first thing to remember about an aquaponic system is that it is being used to grow food in a way that confers several environmental advantages. These include low environmental impact and water use efficiency. Many people are interested in aquaponics because of these principles. Therefore, it is often confounding why people then build systems are that are NOT energy efficient! Many of the system designs available from web sites at present are designed using two pumps or oversized pumps for the application required, which is completely unnecessary and energy inefficient.

Basically, if you locate the outlet from your hydroponic bed slightly higher than your fish tank, then you ALWAYS only require one pump. The water is then pumped from the fish tank, up to the gravel bed, and then returns to the fish tank via gravity flow (which is free and better for the environment!). Simple! Easy! Cheap!

Gravel Bed Hydroponic Component

Gravel beds, whilst not practical on a commercial scale, are the easiest and most efficient hydroponic component you can use for a backyard or hobby system. This is due to several reasons: good plant support, good plant growth & yield, better water buffering and the fact that the gravel acts as both the biofilter and solids filter. For systems not using gravel beds, more water filtering components are required, therefore raising the cost of the system build.

Constant Flow or Ebb & Flow Water Delivery

Many systems at present advocate flood & drain water delivery to the gravel beds. This is done because of several arguments, these being: it enhances root zone oxygen, it saves energy, it assists to mineralise solid fish waste and dissolved nutrients. These are all valid reasons, however, it doesn't mean that constant flows cannot be used. We tested this in replicated experiments and found that constant flows actually improve water quality (in terms of ammonia levels) and lead to increased plant growth rates and yields. However, it must be understood that constant flows can lower dissolved oxygen at the root zone and if solids separation isn't used it can lead to bed blockages and the development of anaerobic zones. Because of this, additional aeration in the fish tank is usually required and a simple solids removal device helps because solids in the system will compete for oxygen. 

Gravel aquaponic systems, if operated in flood & drain modes, do have a high ability to mineralise, dissolve and treat solid fish wastes. However, if fish to plant ratios are too high (see below), gravel beds can clog and lead to toxic (anaerobic) conditions which can kill both fish and plants. Therefore, gravel bed systems do need to be sized correctly to reduce the possibility of this occurring.

We have developed a model to size flood & drain, gravel bed aquaponic systems so that hobbyists have access to the science and engineering that enables confident system sizing. You can find this FREE model (in both metric and USA versions) on our Calculators page..

Water Heating

Aquaponic systems work much better if a constant water temperature is used. The chosen water temperature should suit that required for the particular fish species being cultured and so can be cold (below 12oC), medium (12 - 18oC) or warm (above 19oC). The other reason for keeping water temperatures as constant as possible is because of the biofilter (gravel bed) organisms required to process the dissolved fish wastes from something potentially toxic (eg: ammonia) to something non-toxic (eg: nitrate). The particular bacterial species that convert ammonia to nitrate are adapted to a temperature at which they operate at maximum efficiency. Different bacterial species will colonise the filter depending on the water temperature; cold bacterial species in cold water, warm bacterial species in warm water, etc... If the water temperature fluctuates outside of the range of the bacteria that colonise the media in the bed, then the bacteria can loose efficiency and efficacy. For example, if the temperature requirement of the bacteria in the aquaponic system is in the warm range (eg: between 20o C and 30o C), and if the water temperatures then drop below 18o C, biofilter efficiency is lost, the bugs "go to sleep", and ammonia spikes can occur. This is why many  warm water fish species have a lower feeding rate at lower water temperatures and cold water fish species have a lower feeding rate at higher water temperatures. Therefore, it is always a good idea to try and maintain water temperatures and avoid letting them fluctuate too much. Heating water may be achieved by many methods, like electrical emersion heaters (like those used for aquariums). However, my favored method is to use the SUN. It is very easy to rig up simple solar water heaters for aquaponic systems. In addition, using insulation to insulate fish tanks, gravel beds and pipe work all help to retain heat. Also remember; it is genrally less costly to heat water than to cool it!

Correct Gravel/Media Type

Gravel comes in many shapes and forms, and few people state which gravel is good or bad. For example, I visited a backyard system once where Red Scoria was used. It was very dusty, very red, and was staining the water and pipe worka deep red color. In addition, the Scoria had very sharp edges, which is no good for plant stems and is difficult to work in. The owner could see no problem with this, and was happy to feed the plants and fish to his family. I am not sure of any toxicity associated with the use of Red Scoria, however, some gravels may contain toxic chemicals and compounds, like heavy metals. Therefore, choose gravel carefully and always research any potential toxicity.

The best gravel to use is "washed river gravel". Get it at a size of about 10 mm to 20 mm diameter. Gravel that is too small clogs easily and retards water movement; gravel that is too large is harder to plant into and may not act as an efficient solids trap/filter. People who advocate larger gravel particle sizes often do so because they do not know how to size the media bed for the applied solids load (bed sizing is dependent on a knowledge of correct and efficient solids mineralisation rates for the available surface area of the bed) and so choose larger gravels so they do not clog as quickly with the excess solid waste loads. If gravel/media beds are sized correctly with respct to the fish and feeding rate loads, then gravel beds should last for many many years without detrimental clogging. River gravel has nice, well rounded edges that are easy on both hands and plant stems. Clay balls (Lecca) is also often used in aquaponics and is also an excellent medium for media beds.

Water Testing

pH and temperature are the 2 main basic parameters that need to be tested in aquaponic systems. 

pH - fish, plants and bacteria live at an optimal pH. For fish, this around a pH of 6.5 to 8.0. For plants, this around a pH of 4.5 to 7.0 and for bacteria it is about a pH of 6.0 to 8.0. Therefore, aquaponic systems are a compromise between the pH requirements of the fish and bacteria, and those of the plants. The best pH to run at is around 6.7 to 6.9. This is O.K. for the fish (as it protects against ammonia toxicity), is O.K. for the plants (as it allows them to uptake the nutrients they require for growth) and is good for the bacteria. pH may be tested with simple pH kits obtainable from aquarium stores for less than $20, or by using electronic pH meters.

Many people do not bother to test for pH in their backyard systems. If pH drops below 6.0, the plants usually don't mind and the fish will adapt somewhat over time. However, the biofiltration bacteria do become inactive below a pH of 6.0, so whilst the fish may have adapted they may not be in water of the best quality for their health and well-being. Therefore, I feel it is important to regularly test pH.

Temperature - measuring water temperature regularly allows an understanding of whether the fish are being kept in a temperature range that they are suited to and also allows and understanding of whether the bacteria have the best chance to operate efficiently. Water temeprature may be used as a management tool. For example, when I keep Murray Cod (which likes temperatures of 18 - 24oC), I stop feeding them if the water temperature drops below 18oC or rises above 24oC. This is to protect the fish as they may have digestive problems at water temepratures outside of their ideal range, but also, at these water temperatures outside the acceptable range, the ammonia converison bacteria may loose efficiency and the fish may then be subject to elevated ammonia levels which can become toxic.

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