Aquaponics - A Brief Guide

in Hydroponics Mon Nov 25, 2013 1:47 am
by ozzydiodude • The Weird One | 2.474 Posts | 11542 Points

Backyard Aquaponics
Posted by Pistils at BB

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 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, which is completely unnecessary and energy inefficient. These systems are based upon designs which are around 10 - 15 years old, and that originate in America. These systems are definitely not ideal and have been superseded by more up to date designs.
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, higher 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 to 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 are currently developing 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. We hope to provide this model to you in the very near future.

Water Heating

Aquaponic systems work much better if a constant water temperature is used. The main reason for this is the biofilter (gravel bed). The bacterial species that convert ammonia to nitrate have a range of conditions at which they operate at maximum efficiency. In terms of temperature, this is between 20o C and 30o C. When water temperatures drop below 18o C, biofilter efficiency is lost, the bugs "go to sleep", and ammonia spikes can occur. This is why many fish species have a lower feeding rate at lower water temperatures. Therefore, it is always a good idea to try and maintain water temperatures at or above 18o C in the winter. This 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.

Correct Gravel 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 pipe work. 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 toxic potential!

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. 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

Conductivity, pH and temperature (see above) are the 3 main 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.

Conductivity - this is a measure of the amount of dissolved nutrients in the water. The higher the conductivity is, the more nutrients there are. People familiar with hydroponics call this EC. Good plant growth can be achieved at many conductivities. However, for a good amount of nutrient availability an EC of around 1.2 (1,200 microsemens/cm) is acceptable. However, it must be remembered, plants will grow at higher conductivities.

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