AQUAPONICS TECHNICAL

 

Table of Contents

Introduction

Aquaponics Anatomy

System Choices

System Operation

 

Introduction

This section presents a technical overview of how aquaponics for home use is implemented. Commercial systems for profit are not presented in detail. The biological information in this section has been taken from scientific research. The content is by no means exhaustive and it is recommended that you conduct your own research before building your own aquaponic system.

The University of the Virgin Islands (UVI) has researched plant to fish ratios, stocking ratios, methods and techniques. Their hydroponic versus aquaponic crop trials have proven that aquaponics outperforms hydroponics (note: this comparison would be without seawater dosing of the systems). Trials revealed that hydroponics grows faster than aquaponics initially but hydroponics is overtaken by aquaponics once established. UVI commercial trials have also integrated rabbits into an aquaponics eco-system.

Recirculating aquaculture systems (RAS) have taken fish stocking density from as little as 5kg/ 11lbs up to 80-100kg/ 176-220lbs per 1000 litres/ 220 imperial gallons / 264 US gallons of water in ponds. The following comparisons of various farming techniques are provided as a matter of interest.

Conventional Farming

Advantages

Disadvantages

Hydroponics

Advantages

Disadvantages

Organic

Advantages

Disadvantages

Aquaculture

Advantages

Disadvantages

Aquaponics

Advantages

Disadvantages

The above comparisons are with respect to conventional methods without seawater addition to aquaponics and hydroponics or rock dusting of soil based farming.

 

Aquaponics Anatomy

Aquaponics Elements

Below is a block diagram showing all of the elements of a complex aquaponic system. Hover the mouse over each block in the diagram to view an explanation of each element in the system.

aquaponics block diagram
LED lighting can be used in an enclosed, controlled environment in place of natural light and is cheap to run. The Light Emitting Diodes in the light panels emit the correct wavelengths required by chlorophyll to allow photosynthesis Aeration oxygenates the water. Both the fish and the plant roots require oxygen dissolved in the water for survival Water top up for commercial systems is filtered. For home systems straight from the tap should be acceptable For a home production system a minimum 600 litre fish tank is required. The tank can be just a basic tank or a sophisticated unit which is capable of draining off the coarse solid waste. A diagram of the cylindro-conical tank, which performs this function, is shown in the System Design section The clarifier separates the finer solid fish waste from the water. This is necessary for NFT and raft to prevent build up in the plumbing and hydroponics. The sump is the lowest point in the system where the pump is located. The pump should turn over the total volume of the fish tank twice every hour. Bio-filtration creates a large surface area for bacteria to adhere to where the ammonia is converted into nitrate by the bacteria. In a media bed system the media in the hydroponics section becomes the bio-filter. Since NFT and raft systems have no media in the hydroponics section a dedicated sump containing some form of solid media is required to harbour the bacteria necessary for the conversion processes in aquaponics. This is the plant growing area. The three types currently in use globally are are described in the System Selection section below. Refers predominantly to the fish waste that collects in the fish tank. In a heavily stocked system it is usually drained off daily and can be used as an organic fertilizer. Degassing is the removal of harmful gasses from the water. This process occurs by breaking up the water into finer particles before it returns to the tank. The more gasses removed the more room for dissolved oxygen under atmospheric pressure. Water return falling into the tank can provide degassing and aeration in a basic aquaponic system.

Aquaponics Biology

Nitrification/De-nitrification

Fish waste leaves ammonia in the water. If this is allowed to build up it eventually kills the fish. The ammonia is eliminated by bacteria converting it into a form that becomes a natural fertilizer for plants. Nitrosomonas bacteria convert the ammonia to nitrite. Nitrobacter then convert the nitrite to nitrate. The nitrate is the fertilizer taken out of the water by the plants effectively cleaning the water for the fish.

bacterial action

In a poorly maintained system anaerobic bacteria can start to produce and cause de-nitrification back to ammonia. This is caused by a lack of aeration of the water as it is the oxygen from the air that kills the anaerobic bacteria. An increase in ammonia causes the water to turn milky.

Bacteria levels decrease in winter. Levels will decrease by 50% for every 10° Celsius/ 50° Fahrenheit drop in water temperature. Since the bacteria are required to convert the ammonia you would need to double the size of the hydroponics to double the bacteria colony size to cater for this drop in temperature. However, this coincides with the slower metabolism of fish generating less ammonia through the winter months and is corrected, to a certain extent, by nature. No bacterial activity can survive at 4° Celsius/ 39° Fahrenheit or below and they also die in excessive heat.

Nitrogen, hydrogen sulphide, methane and carbon dioxide gases are also generated in the system. Degassing of the water by aeration releases these gases and oxygenates the water at the same time. In an enclosed area, releasing carbon dioxide from the water into the air is beneficial to both fish and plants. Plants absorb carbon dioxide from the atmosphere and release oxygen into the atmosphere. The fish and plant roots obtain oxygen through the aeration process. An enclosed environment allows channeling of carbon dioxide to the plants for more efficient photosynthesis and faster growth.

oxygen cycle

In an optimized aquaponic system 1kg of fish food input can result in the production of 1kg of fish and 7kg of plants.

 

System Choices

System Selection

System Types

There are three types of aquaponic systems currently in use throughout the world:

NFT (Nutrient Film Technique)

NFT is a widely used system in commercial hydroponics because of its efficiency and high production rates. It consists of channels containing seedling tubes for the plants. The seedling tubes contain a form of soft media. A film of water just a few millimetres deep runs through the plants’ roots in the bottom of the channel. The water is drawn up into the root system by capillary action. This system allows the roots to get oxygen and nutrient rich water at the same time. Because of the relatively small amount of water, (one sixth of the water a raft system contains) it loses its buffer ability so keeping the water parameters within limits is more critical than the other types of aquaponic systems. NFT has the same nutrient loading for less water due to the higher concentration and more efficient use of the water. Evaporation causes nutrient concentration to increase which creates the following abilities:

A typical water flow rate in NFT is one litre/ 1.76 imperial pints / 2.114 US pints per minute, approximately 3mm/ 1/8 inch deep, through a trough 12 to 18 metres/ 39 to 59 feet long. Because of its high-tech nature NFT requires more components in the system which makes it more expensive to set up initially.

Advantages

Disadvantages

Photo examples of NFT systems

Internet Images

Raft Systems

Extensively researched by the University of the Virgin Islands, raft systems consist of polystyrene sheets with holes for the plants to grow in. The rafts float in troughs with the plants’ roots permanently in the water. This creates the need to continuously aerate the water. Fish are generally kept in tanks separately from the channels as they will eat the plants’ roots. If they are kept in the raft channels some form of barrier needs to be established between the fish and the plants. Raft aquaponics will produce approximately 100 fruiting plants for an input of 60 to 100 grams/ 2 to 3.5 ounces of protein per square metre/ 1.2 square yards. The extensive research conducted by the University of the Virgin Islands on their raft aquaponic systems is presented in this link:

UVI Raft System

Advantages

Disadvantages

Media Filled Systems

Media filled beds are a simple system compared to NFT and raft which is why they are popular as a residential backyard aquaponic system giving them extensive Internet support through websites and forums. The simplest form consists of a fish tank and a grow bed. The fish tank generally doubles as the sump where the pump also resides and the media bed also becomes the biological filter. It is as simple as the water being pumped up to the media bed and flowing back into the fish tank by gravity. The fall of the water returning to the tank generally creates enough aeration and degassing to support the system without the need for a separate aeration pump. Systems of this type can be purchased ready-made for back yards or compact patio installations. Patio installations can have the media bed mounted on top of the fish tank to conserve space.

Advantages

Disadvantages

Comparisons

Some plants are more suited to one type of system than another (e.g. lettuces are better in NFT and tomatoes in media). There is no reason why you can’t have a hybrid system although this deviates from the simplicity of running one type of system. NFT and raft rely solely on water flow and quality to maintain system health and require daily maintenance and monitoring of the system components. Media filled systems require less daily maintenance and monitoring.

NFT and raft require a solids filter (clarifier). Gravel beds act as the solids filter in a media filled system so a separate filter is not essential although it will reduce maintenance time and effort. Solids collect in gravel beds and break down causing mineralisation, which makes the system more efficient by releasing trace elements into the system. Even so the beds will need cleaning periodically and adding a solids filter at the pump inlet dramatically reduces the necessary cleaning of media beds.

NFT and raft systems require a separate bio-filter for the bacteria to colonise on and break down the ammonia whereas the gravel in a media filled system acts as the bio-filter for the bacteria to colonise on. Bio-filter infill for NFT and raft is generally in the form of a purpose-built plastic material. (There is no reason why something natural like scoria shouldn’t be used. It may even have a greater surface area per unit volume, due to its porosity, than artificial purpose-built material and is readily available at garden centres.) The independent bio-filter and clarifier allow NFT and raft to be more suitable for commercial use as the hydroponics and fish tanks can be separated and run independently of each other for servicing and isolation of problems.

System Design

General

System design is focussed on aquaponics for home use so NFT and raft will not be represented in detail as they are predominantly for commercial applications. This section is specific to media filled aquaponics and covers design only. System build is not illustrated as parts and materials vary worldwide and build configurations are personal choice. Extensive information for build ideas can be found on the Internet.

Design Considerations

System Configurations

The simplest configuration in media bed aquaponics consists of a pump, a tank and a grow bed. The pump uses the tank as the sump and pumps the water up into the media bed which then drains back into the tank via gravity. The media bed acts as the bio-filter and solids filter.

grow bed drain configuration

Adding a solids filter to the inlet of the pump will reduce cleaning maintenance on the media bed extensively. A system of this type can have the media bed mounted above the tank which reduces the footprint and makes it suitable for smaller areas such as patio or courtyard installations. The use of the cylindro-conical fish tank shown below can make cleaning much easier as its integrated sump collects the solid waste which is easily drained off. The trade off here is that the seawater dosing is depleted and the seawater will need to be rebalanced with every solids drain-off. This can be reduced by straining the drain off and returning the water to the system.

tank drain configuration

In this configuration the pump needs a separate sump to create the low point in the system and pumps into the tank instead of the grow beds. The disadvantage is that it takes up more space due to the extra sump component and the fact that the growing area has to be located below the tank level for gravity flow. This system is more suited to larger areas and is particularly suitable for NFT systems as the sump can create extra water buffering. The operation of the cylindro-conical tank is described in the "Tank" section below.

Enclosure

An enclosed aquaponic system will provide better food production due to environment control. A simple greenhouse can be relatively cheap to construct but a closed room or insulated shipping container using purpose built LED lighting has the potential to allow total control.

The benefits of enclosures:

On the other side the negatives are:

Tank

A 600 litre/ 132 imperial gallon / 158 US gallon tank should be the minimum requirement for a home system. A tank is nothing special unless it is tailored for a purpose. The cylindro-conical tank is such a tank. This design is the most effective method for collection of the solid waste produced by the fish.

cylindro-conical tank

The tank is constructed with two concentric standpipes in the centre. The outer standpipe has openings at the base to let solid waste through and fall into the integrated sump. The openings must be small enough to prevent fish from entering as this is also the water outlet. The inner standpipe is the tank’s water outlet pipe to the hydroponics area. It also keeps the water level constant in the tank. The pump’s outlet into the tank is positioned at an angle such that the pressure causes the water to circulate. The slower circulation in the centre allows the solid waste to fall to the bottom. The conical floor channels the waste to the centre where it settles in the sump and is drained off daily. To avoid the need for a separate aeration pump for oxygenation and degassing a venturi can be built into the tank’s water entry point to draw air in with the pumped water.

Hydroponics

The type of plant container can vary depending on what you are growing. Troughs containing solid media are suitable for leaf vegetables. Deep tubs containing an easily displaced soft media are needed for root vegetables. A shallow tray with no media or a thin layer of mulch is sufficient for growing grasses such as the popular choice of wheat grass.

Media

Solid types for leaf vegetables: gravel, scoria, clay balls

Porous media is more space efficient than non-porous media due to its increased surface area for bacteria to colonise on. As John Hamaker states (with respect to rock dust) in The Survival of Civilisation, “…a one pound stone might have a surface area of 12 square inches. Ground to 200 mesh, it would have a surface area of 8 acres.” Scoria and clay balls have that extra surface area on the inside due to their porosity and also have anaerobic zones as well as aerobic zones so do two jobs at once.

Soft types of media suitable for growing root vegetables are perlite, coco-peat (coir) and rock wool - to mention a few. All have good water retention during water flow failure. Perlite is generally cheapest and rock wool the most expensive. Perlite is soft and light but more difficult to work with.

Plumbing

Pipe diameter is critical to prevent the settling of suspended wastes in the pipes resulting in reduced flow. Living organisms will also attach themselves to the inside of the pipe. Design a system with screw fittings and barrel union joints in case you need to dismantle the entire system for cleaning. For example if you cap the end of a pipe install a screw cap instead of a glued cap. Even if you have a solids filter pipes can still accumulate scale or sediment.

Pumps

Depending on how the system is configured the pump may be housed on the floor of the fish tank, in a sump or external. Submersible pumps, housed in the tank or sump are generally low pressure, low flow, cheaper to run, cost less and run quieter. The heat from the pump can also help heat the water. Centrifugal pumps are external. They are high pressure, high flow, noisy, cost more and are costly to run. Airlift pumps are cheaper to run and aerate the water at the same time. The Internet has ample information on how to build your own. This Youtube video illustrates the basic principle of an airlift pump.

Keep a spare pump on hand in case your operating pump fails. An option of building backup into your system is to run two smaller pumps in parallel to do the job of one larger pump. This way if one pump fails you still at least have water flow. Solar or battery backup is also an option for building a fail-safe system in the event of power failures.

Solids Filter

A solids filter is not necessary on a media bed aquaponic system. The media bed itself acts as the filter. However this means higher maintenance in the form of cleaning the media. Adding a solids filter will reduce this task extensively. For a home-made filter foam rubber does a sufficient job, so does fine weave plain polyester curtain fabric. In a heavily stocked tank the surface area of the solids filter can clog in a short period of time so you need a filter with a large surface area to cope with long periods between filter cleaning. Various types of mechanical screen filters are available but cost is a limiting factor. This builds a case for the cylindro-conical tank with its integrated solids collection sump. There is no filter surface to clog so system down time is less.

Auto-siphon

An auto-siphon creates a flood and drain cycle in the media bed for aeration. The aeration is necessary for the oxygenation of plant roots and the survival of bacteria. Illustrated below are two types of auto-siphons.

The simplest type of auto-siphon is the loop siphon below. It is simply a piece of flexible hose on the media bed outlet. It is easily adjustable to set the high water level. When the water reaches the top of the loop the suction of the water in the hose outlet takes over and drains the media bed down to the low water level. At this point the hose inlet takes in air and breaks the suction. It can also be installed on the inside of the media bed. In an internal installation the low water level is also adjustable. The top of the loop determines the high water level and the end of the hose can be adjusted for the low water level.

loop auto-siphon

The bell siphon is no different in principle from the loop siphon. It is just a different structure which is located inside the media bed. The siphon pipe in the centre sets the high water level. The openings at the bottom of the bell cylinder set the low water level. The bell cylinder is a piece of pipe (usually PVC) with an air tight top and rests on the floor of the media bed so it is easily removable for servicing. The outer cylinder can be made from rigid mesh or a larger, perforated piece of PVC pipe. It should be fixed to the media bed floor as its function is to prevent media from resting against the bell cylinder allowing it to be removed for maintenance.

bell auto-siphon

Whichever auto-siphon is used the diameter of the siphon pipe needs to be "tuned" to some degree with the media bed inflow from the pump. If the siphon outlet diameter is too big the suction won’t begin. If the diameter is too small the inflow will be faster than the siphon can extract the water and the media bed won’t drain. An adjustable aperture on the outlet allows the fine tuning for different pump flow rates.

Automatic Water Top-up

If you live in climatic conditions that experiance a high evaporation rate an automatic water top up function may be beneficial and may be essential for NFT due to its lower water buffering ability. A float valve should ideally be located in the same location as the pump i.e. the sump or fish tank.

Overflow

If you have a system in an open area susceptible to high rainfall an overflow in the tank may prevent fish loss. A cylindro-conical tank system doesn’t have this problem but an overflow can be installed in the pump sump.

System Specifics

Adding Another Dimension

Aeroponics is simply growing plants in air in a misted enclosure. Potatoes are capable of being grown in air using this method (they’ll grow in your pantry cupboard in the right conditions). The air in the enclosure is misted with water from the aquaponic system, vegetables absorb the nutrient rich moisture from the air and excess water is returned to the aquaponic system in the same way as in media beds. Misting units should be readily available as they have been used by plant nurseries in green houses for humidification for many years.

Fish Selection

General

Unless you have an enclosed climate controlled system, select the species of fish to suit your climate. If your climate varies extensively from summer to winter you can alternate between two species of fish to suit the seasonal temperature change. Around 22° Celsius/ 72° Fahrenheit is an average temperature for most fish. If you need to alternate between summer/winter species take water temperature readings weekly throughout the year and plot them on a graph to determine which species are most suited to your climate and which months to switch between species.

Popular Choices

Tilapia is a fast growing fish and is the most popular choice for home systems in USA. They can breed easily in aquaponic systems so restocking with fingerlings after initialization is generally unnecessary. They are also suitable for tropical conditions and can be chemically sex-reversed to produce fast growing all-male cohorts. Tilapia are a very salt tolerant species with tolerance levels well in excess of the requirement for seawater dosing of freshwater aquaponic systems. Optimal temperature range for the best growth rate is around 28-30° Celsius/ 82-86° Fahrenheit with tilapia aurea (blue tilapia) being the most cold tolerant suitable for cooler climates.

Barramundi and trout are popular choices as a faster growing fish and can be alternated from summer to winter. Barramundi is suitable for warm seasons and tropical climates whereas trout is strictly a cold water fish.

Atlantic salmon is a high quality fish that is capable of being farmed in fresh water with a very acceptible growth rate.

Restrictions

Check these points with your authorities before you start.

Otherwise you’re free to do as you please to support your own survival!

Considerations

Parameters of Popular Aquaponics Species

pH comparison chart
temperature comparison chart

Barramundi

  • Dissolved oxygen: 5mg/l
  • Temperature: 24 to 32° Celsius/ 75 to 90° Fahrenheit, optimum 28° Celsius/ 82° Fahrenheit
  • pH: 6 to 8
  • Salinity: 0 to 32ppt
  • Ammonia: 0 to 0.9mg/l

Silver perch (omnivorous: good for high densities)

  • Dissolved oxygen: 5mg/l
  • Temperature: 20 to 24° Celsius/ 68 to 75° Fahrenheit
  • pH: 6 to 8
  • Salinity: 0 to 8ppt
  • Ammonia: 0 to 0.9mg/l

Jade perch (high in oils)

  • Dissolved oxygen: 4mg/l
  • Temperature: 18 to 28° Celsius/ 64 to 82° Fahrenheit
  • pH: 6 to 8
  • Salinity: 0 to 4ppt
  • Ammonia: 0 to 0.9mg/l

Trout (for cooler climates or seasons only)

  • Dissolved oxygen: 6mg/l
  • Temperature: 12 to 18° Celsius/ 54 to 64° Fahrenheit, optimum 15° Celsius/ 59° Fahrenheit
  • pH: 6 to 8
  • Salinity: 0 to 32ppt
  • Ammonia: 0 to 0.08mg/l

Tilapia

  • Dissolved oxygen: low tolerance (3 to 5mg/l for maximum efficiency)
  • Temperature: 28 to 30° Celsius/ 82 to 86° Fahrenheit optimum; minimum 21° Celsius/ 70° Fahrenheit
  • pH: 7 to 8
  • Salinity: Varies with type. Very high tolerance with respect to a fresh water aquaponic systems.
  • Ammonia: 0.6mg/l

Plant Selection

Selection Considerations

General

Different plants require different minimum nutrient concentration levels in the system to support growth. The nutrient level is generally measured in units of electrical conductivity (EC) in micro Siemens/centimetre. The higher the EC, the higher the level of nutrients in the system. A higher EC supports the growth of more fruiting types of plants such as tomatoes and cucumbers. Higher fish loadings are required to support fruiting plants in a non-seawater dosed system.

Different vegetables are optimally suited to different systems. For example tomatoes are more efficiently grown in media beds and lettuces are more efficiently grown in NFT. This doesn’t mean that you can’t grow them in other types of systems.

High water content plants such as melons draw a lot of water from the system. This may necessitate the installation of an automatic top up feature mentioned in the System Design section, particularly if you are trying to grow this type of plant in NFT with its low water buffering capacity.

Some plants have an enormous root mass and are generally unsuitable for aquaponics. One of these plants is celery. If you choose to experiment be sure to use a large dedicated tub that you can integrate into your system. Use a media such as coarse sand that is easy to hose out of the roots. Gravel is too difficult to separate in a large root mass situation.

Temperature

Select plants to suit your climate unless you have a controlled climate enclosure. Even then you may still need to alternate types from summer to winter. The average optimal temperature for most plants is around 26° Celsius/ 79° Fahrenheit

pH

Plants get most of their nutrient uptake in the pH range of 6.5 to 7.5.

Nutritional Value

Information on the complete element content of plants is difficult to find. Generally only minerals labelled as essential are listed. Many trace elements are not considered important as they have been labelled non-essential even though, with many, their functions in our bio-chemistry are still unknown. Fish food will provide only a limited amount of nutrients for the system via the fish, a long way from the 92 elements that our immune systems are required to have by nature. This is where dosing your aquaponics with seawater comes into play. Not all plants will take up all 92 elements. There are claims that chlorophyll takes up all 92, however conclusive evidence to support this claim is difficult to find as scientists generally don't experiment with seawater as a fertilizer as Dr. Maynard Murray did. If you find that this is the case wheat grass appears to be a popular choice for improved health.

Parameter Examples

Bok choi

Tomatoes - require higher stocking density of fish

Basil - rapid growth rate (3 weeks to mature)

Chives

Cucumbers

When you acquire your seeds, verify that they are certified organic and not genetically modified otherwise your plants will be genetically modified which may be detrimental to the development of optimal health.

 

System Operation

System Start-up

Water

Aquaponic systems can be started without fish by adding bacteria and fish feed for trace elements for the plants. Obtain fish feed from a known quality source. Don’t assume all feed is clean and free of contaminants. Over the counter bacteria is diluted which is why it is so much cheaper than bacteria concentrate. A well established home aquarium will also have bacteria that can be used. The risk is that you could be introducing diseases or contaminants right from the start.

The natural method is to put the fish in and put some feed in. When the water goes cloudy stop the feed for a day or two. When the water starts to clear it indicates that the bacteria have started to generate. Don’t over feed the system. A slightly yellow-brown tinge in the water indicates aging water and is a good sign that the required bacteria are present. Nitrosomonas (ammonia to nitrite) double every seven hours in optimal conditions. Nitrobacter (nitrite to nitrate) take about thirteen hours to double. It takes around three to four weeks for bacteria to colonize a system in optimal conditions which follows approximately forty days of ammonia build up. It can take six to nine months for a system to fully establish.

A dedicated seawater aquaponic system can take nine to twelve months to fully establish. This indicates that adding seawater at the beginning may slow the colonisation of bacteria in the system even though seawater contains nitrosomonas and nitrobacter plus the full spectrum of elements for optimal health of the system (just another aspect of aquaponics that needs more time consuming research). The dosage rate for seawater is covered in the System Maintenance section.

As a point of interest the element content of seawater is displayed in this link to an interactive periodic table:

www.marscigrp.org/ocpertbl.html

pH

The optimal pH range for nitrosomonas is 7.8 to 8.0 and for nitrobacter is 7.3 to 7.5. Different parts of an aquaponic system will naturally run at different pH levels to accommodate the difference required for each bacteria. The optimal pH range for plants to take up nutrients is 6.5 to 7.5. With the these ranges in mind the optimal pH range for the entire system is 7.0 to 7.5. The natural methods of adjusting pH are:

Plants

Starting plants from seed is the preferred option to avoid disease. Media filled beds can be directly seeded. NFT and raft have to be germinated in a media before being transferred into the system. If seeds are germinated before being introduced into the hydroponics they can be germinated in a tray of soft media initially using water from the fish tank. As it evaporates top up the tray with fresh water to avoid excessive salinity. On the other side don’t let the seawater level drop too low as it will weaken the resistance in the system leaving the seedlings susceptible to pests and disease.

Fish

Don’t introduce fish from someone else’s system without quarantining them first. To be sure give the fish a salt bath. When they start to roll take them out and put them back into fresh water. This is not effective with fish that can live in both salt and fresh water. In a fully recirculating system start with larvae as opposed to big fish. Larvae don’t have the organisms living in the gut that big fish have so won’t introduce those organisms into the system. Acclimatise fish slowly to the new environment including light. Take water readings before acclimatising larvae (pH, temperature, salinity, ammonia and dissolved oxygen) to ensure that it is suitable for their habitation. Salinity, ammonia and dissolved oxygen should not be an issue at the system start up stage. The maximum stocking density of fish is around 40-50 per 1000 litres/ 220 imperial gallons / 264 US gallons of water.

You can use one of two methods of stocking:

If you get the fish to vegetable balance correct then focus on looking after the fish. The plants will then require little maintenance.

System Maintenance

Water

An aquaponic system heavily stocked with fish should have the pump running 24hrs a day to prevent the water from turning rancid. The optimal water temperature for bacteria is 29° Celsius/ 84° Fahrenheit. Bacteria cannot survive at or below 4° Celsius/ 39° Fahrenheit and they will also die in excessive heat. Bacteria levels decrease by 50% for every 10° Celsius/ 50° Fahrenheit drop in water temperature. This means you would need to double the size of the biological filter capacity (hydroponics area) to cater for the reduction in temperature. However, this drop in temperature coincides with the slower metabolism of fish generating less ammonia through the winter months and is corrected, to some extent, by nature. Since optimal temperatures for bacteria, plants and fish are slightly different you need to determine the optimal temperature yourself for your choices of plants and fish.

Some aquaponicists grow duckweed in the fish tank to strip out the nitrogen. This prevents algae from growing in the tank. Whilst this may be beneficial in some cases it will eliminate a food source for any algae eating fish in the system, hence eliminating the algae in the some systems may prevent optimal health of the system. Excessive amounts of algae should be manually removed as it can be a hinderance to the fish by getting caught in their gills. If duckweed is used to reduce nitrogen segregate it from the fish. It may also be food to them.

If you filter off the solid waste from the system don’t discard it. It can be used as fertiliser for soil bound plants in your garden. The University of the Virgin Islands dehydrate their fish solid waste and sell it as organic fertiliser.

In a poorly maintained system, which is reaching optimal health, anaerobic bacteria can start to produce and cause de-nitrification back to ammonia. This is caused by a lack of aeration of the water as it is the oxygen from the air that kills the anaerobic bacteria. An ammonia problem in the fish tank is evident when the water is milky. The water has a slightly yellow-brown tinge when in good health.

Seawater Addition

Chemical fertilisers lack nutrition as they provide only a small number of elements from the complete spectrum. Organic fertilisers are only as good as their sources most of which have been lacking elements in the first place as a result of global soil mineral depletion. Fish food generally provides a limited number of nutrients for the system through the fish. Seawater puts all naturally occurring elements into the system in the correct balance. Seawater also contains the bacteria necessary for the system; nitrosomonas and nitrobacter. If you don’t have ready access to clean seawater you can purchase a product like Ocean Solution or similar. Be wary of collecting surface seawater. Surface water may be low in some elements as a result of sea life consuming the elements as the seawater moves up from the ocean floor. Surface water may also contain human induced contaminants. However, it may be better than nothing. Failing that you can use unrefined sea salt. It still contains most elements found in seawater and is far better than commercial fertilizers. Dr. Maynard Murray used reconstituted sea solids in his hydroponic experiments. In its unrefined state sea salt’s appearance is off-white, not pure white. Be careful what you buy.

The optimal seawater dosing rate for aquaponics is still unestablished as it is still largely unexplored by researchers and may depend on the salinity tolerance of the plants you choose. Most fish suitable for fresh water aquaponics will be capable of tolerating the salinity level you need to provide the appropriate nutrient level for your plants. Keep in mind that it takes an EC of 2000µS/cm to support fruiting type plants. When dosed with seawater this relates to a salinity level of around 1.00ppt (1000ppm). Dr. Murray’s reconstituted sea salt dosage rate in hydroponics was 112lbs to 10,000 gallons of water. Assuming Dr. Murray was using units of US gallons this equates to a salinity level of approximately 1.31ppt (1310ppm or EC of 2560µS/cm) using unrefined Celtic sea salt in reverse osmosis filtered water with an initial salinity reading of 11.8ppm (EC of 8.2µS/cm). Our own aquaponics has run successfully at around 1.5ppt using mains supplied tap water.

Research on vegetable salinity tolerance pertaining to aquaponic systems appears to be non-existant at this stage. To determine the optimal salinity level for your system you may want to assess the figures in the following research which has been conducted on soil based vegetables. The readings don’t appear to take into account any salinity already existing in the soil.

USDA Agricultural Research Service

Salinity level in aquaponics will increase with evaporation so the system water level needs to be kept topped up to its optimal level. This can be critical in NFT due to low water buffering ability and can be detrimental to low salt tolerant plants like strawberries and carrots. An auto top up function may be necessary for high evaporation climates and is recommended for NFT in any situation.

Plants will take up nutrients from the water at different rates so it is beneficial to replace the system water progressively in small amounts to replenish the complete spectrum of elements and keep them in balance. You can use the discarded nutrient rich water on your soil bound plants.

System Monitoring

Basic Measurements

For a home system the basic measurements are all you need for monitoring. As long as the water return falling into the tank or sump is creating sufficient aeration it will also degas the water. The system flow rate is determined by the pump you choose and plumbing restrictions. Measuring pH, temperature, salinity and electrical conductivity can be done with a compact multi-functional instrument such as Eutech and Extech instruments.

Temperature and pH are straight forward measurements.

Websites express salinity in varying units. Salinity is in parts per thousand (ppt) or parts per million (ppm) on the display of a Eutech instrument.

Applying EC can be confusing. Here are the conversions: deciSiemens per meter (dS/m) = milliSiemens per cm (mS/cm). MilliSiemens per cm multiplied by 1000 = microSiemens per cm (µS/cm) = Electrical Conductivity units (EC).

Advanced Measurements

If you have a more elaborate system you may need to take advanced measurements in addition to the basic measurements. This will require more expensive equipment and is essential for a commercial operation. An oxygen meter for example needs to be programmable to altitude as oxygen level is altitude dependent.

Fish

Different species of fish have different habits. Familiarise yourself with the habits of the species in your system. To determine if a system is stressed observe the behaviour of the fish first thing in the morning. If any fish appear diseased quarantine them from the system immediately. Lethargic or fungus affected fish is usually an indication of poor water quality and can be due to something as simple as slow flow.

A salt bath is a conventional treatment for fungus. Yabbies can also get fungus infection due to poor water quality. Fresh water fish can only be kept in a salt bath for a short time. When the fish starts to roll take it out immediately and return it to fresh water.

A well maintained seawater dosed system should keep fish healthy anyway. If the parameters are allowed to drift out of acceptable limits it may provide an environment favourable to fungus and parasites. If this should occur a quarantine tank on standby with the maximum tolerable level of seawater for your species can heal the fish. All other parameters should be the same as your aquaponic system. Depending on how sick the fish are healing may take several weeks.

If your fish will feed on floating food use it in preference to sinking food as there is less chance of the food being sucked into the filter and wasted. Sift the fines out of the fish food because they pollute the water. Feed the fish 3% of their body weight per day. Fingerlings should be fed up to 8% because of their fast metabolism and then reduce the rate as they grow. Fish are fed up to three times a day especially when they are small. Only feed as much as they can eat in 10 minutes to avoid fouling the water. Smaller fish should be fed smaller amounts at more regular intervals. Bacteria levels drop off in winter so less feed is needed.

Fish that are omnivorous (not carnivorous) such as tilapia require less protein in their food. If protein is overdone it can cause liver problems in the fish.

Research the natural food source of your choice of fish and be aware that researchers are working to develop genetically modified (GM) soy bean as a fish food additive to produce the Omega 3 and Omega 6 long-chain fatty acids required in human diets. Refer back to "The Nightmare of GM Foods" in the Immune System page. This may affect your choice of commercial fish food.

Plants

The amount of vegetables is proportional to the amount of protein fed to the fish (e.g. 56 grams/ 2 ounces of food will sustain 2 square metres/ 2.4 square yards of production area containing 72 lettuces).

Don’t handle plants in your aquaponic system after handling plants outside of the system as this may introduce disease.

pH 6.5 to 7.5 is the range in which plants get most of their nutrient uptake. Outside of this range plants won’t absorb nutrients efficiently and growth will slow. However pH should be kept in the range of 7 to 7.5 to suit the whole system. Media filled beds don’t have as much problem with pH as other types of systems as the gravel buffers the level to some degree.

Seawater can be applied to plants in dilute solution as a foliar spray. If you need to run your aquaponics with a lower seawater dose to suit some low salt tolerant vegetables you can supplement higher salt tolerant vegetables using this method. The stomata on the underside of the leaves are open around dawn and dusk and can absorb the sprayed solution in a short period of time. Too much seawater in the system or as a foliar spray will kill the vegetables just as too much commercial chemical fertilizer on field crops will burn or kill the crop.

A few bug holes in vegetables indicate no chemical sprays; however pests can be controlled in various ways either naturally or organically.

Contrary to the above, you shouldn’t have much trouble with pests when you have the seawater dosing level correct. Bugs generally only attack plants in poor health as is the case with humans who have poor immune systems. Nature has its way of balancing out and eliminating the weak.

General

The following points should not be critical if your system is dosed appropriately with seawater giving your plants strong disease resistance as researched by Dr. Maynard Murray. However it is still good practise.

 

Harvesting The Product

Plants

Harvesting of plants is straight forward. Either pull out the whole plant or trim off what you need as you need it. It is more difficult to separate the roots of plants grown in clay balls than those grown in gravel.

There is one very important point to consider before harvesting your plants. Phytochemicals are stored in the roots and stems of the plants and only transfer into a fruit or vegetable within the last 48 hours of ripening. If the fruit or vegetable is green picked as they appear in supermarkets this is robbing your immune system of nutrients.

Let some of your plants go to seed for subsequent crops. In a seawater dosed aquaponic system this will enable the maximum number of elements to be present in the plant right at the beginning of the growth cycle.

Fish

Harvesting fish is not as straight forward as plants. They need to be purged to clean out the gut track before harvesting due to the build up of tannins. Carnivorous fish have a shorter gut track than omnivorous fish so will purge faster. For example it will take 4-5 days for barramundi against 5-7 days for silver perch.

Procedure:

 

Last update: 21-06-2018