Aquaponic media bed sizing calculator – USA Ver 2.0
1
Aquaponic Media Bed Sizing Model - USA
Written by Wilson Lennard PhD
Version 2.0, September 2012
Welcome to Version 2.0 of the Hobby Scale Aquaponic Media Bed Sizing Calculator. The calculator
has been updated in a number of ways. The first change you will notice is that two of the outputs
have been removed; the biofilter volume output and the bed surface area for fruiting plants output.
The biofilter volume output has been removed because in all cases, when the media bed is sized for
the fish feed to bed area ratio (based on the UVI ratio’s), the output gives a surface area that when
using a 300mm deep media bed will always meet the biofiltration volume requirement. The fruiting
plant bed surface area output has been removed because the original leafy green plant bed surface
area is most often used, and if fruiting plants are to be grown, then the far lower planting density of
fruiting plants (when compared to leafy greens) means that in the vast majority of cases, all things
even out.
The major upgrade to the calculator has been an improvement to the mathematics used to calculate
the surface area of the bed required to mineralise the fish solid wastes. In the original version, due to
the complex “log” based mathematics used, there was a “black hole” that appeared at lower fish
densities which manifested as an inconsistency in the output whereby the surface area output could
in some cases actually drop when the fish density rose. This has now been rectified and so no “black
hole” should now be present in Version 2.0 and the bed surface area will rise as the fish density does.
The other change is that there has been a slight “tweaking” of the UVI feed rate ratios. This is
because I have gained more knowledge and insight into how much nutrient can be contributed by
leaving solids in the system to mineralise and breakdown in the media bed.
This current explanation document has also had several small changes done to it to reflect the
changes in the calculator as outlined above. The major addition is a short discussion on how the
addition of worms to the media bed MAY, or MAY NOT affect the media beds ability to
breakdown and mineralise fish waste solids.
I hope this calculator assists with your hobby scale aquaponic designing. Aquaponic media bed sizing calculator – USA Ver 2.0
2
Introduction:
Many backyard, hobby and domestic aquaponic system users, designers and builders are confused
about the ratio between the fish tank size and the media bed size (gravel, Lecca etc…) in their
systems. There are many “rule of thumb” approaches to this fish tank to media bed ratio, but these
are not based on established scientific, technical or engineering principles. This document and the
attached Spreadsheet calculator is an attempt to provide a useable method and model so that any
hobby or domestic scale aquaponic system user or designer may have a guide to design and size their
systems. This model and the outputs it produces are based on accepted and established scientific
and engineering principles that are directly applicable to the design of aquaponic systems.
Distribution of the Model:
This model has been produced for FREE use by anyone who wishes to use it. It can be downloaded
for FREE at www.aquaponic.com.au and other web sites. This means that the model can be
effectively shared between users and you are welcome to distribute it, unaltered, at your discretion.
The model and associated information (ie: how to use…) document is not to be sold by or to any
person, organisation or party. The model has been produced and is available in both Metric and
USA versions. All I ask is that if you use this model in a multi-user (ie: teaching classes or you are a
system sales company) capacity, that you properly credit me as the writer and distributor of the
documents.
The Model:
The Spreadsheet model that accompanies this document is a tool that allows you to size the area of
the media bed in your system based on a number of important inputs. In addition, the model
provides outputs for a number of parameters. Basically, the model will size the surface area of the
media bed for you based on whether you wish for the bed to operate as a biofilter or as a solids
mineralisation filter or as a plant growing component or a combination of all three. It is up to you,
the user, to decide which bed size is best for your situation. However, it is recommended that the
largest bed size given by the model will be the best for your system. Aquaponic media bed sizing calculator – USA Ver 2.0
3
Component Ratio – plant growing area requirement:
It is often thought that the ratio in aquaponic systems is between the fish tank volume and the plant
grow-bed surface area or volume. However, this is not correct. The ratio is actually between the
daily amount of fish feed that enters the system and the grow bed surface area. This is confirmed by
the years of research conducted at the University of the Virgin Islands by Dr James Rakocy and his
team which has ascertained a range of ratios for daily feed input to plant growing area for deep flow
based aquaponic systems.
The UVI ratios are:
1. For leafy greens – 0.20 oz/ ft2
/day
2. For fruiting plants – 0.33 oz/ft2
/day
As can be clearly seen, plant growing area is directly linked with the daily fish feed input to the
system. These ratios are also appropriate for media based backyard and hobby scale aquaponic
systems, so the attached model allows you to size the grow bed area based on the plant growing area
requirement as set by this UVI ratio. Aquaponic media bed sizing calculator – USA Ver 2.0
4
The UVI model is based on fish that eat 32% protein feed (Tilapia spp.). However, many fish also
used in aquaponic systems eat higher protein content feeds (45%). Therefore, the UVI ratio in the
attached calculator has been re-calibrated for situations were high protein content fish feeds are
chosen. In addition, most backyard and hobby aquaponic systems use the media bed as a place for
mechanical filtration and mineralisation of solid fish wastes and this approach will supply extra
nutrients to the system (the UVI system design removes the majority of the solids from the system
very quickly). Because of this, the fish feed to plant growing area ratios have also been re-calibrated
to take solids inclusion to the system into consideration when calculating plant growing area.
Component Ratio – biofiltration requirement:
The media bed in hobby and backyard scale aquaponic systems also acts as the primary location for
biofiltration; the bacterial assisted conversion of potentially toxic fish waste ammonia to non-toxic
nitrate. In actuality, the biofiltration requirement is not usually relevant to media based backyard and
hobby scale aquaponic systems, because there is always an excess of media in the bed when the UVI
ratios are followed and therefore, the biofiltration media volume requirement is always met.
Component Ratio – solids mineralisation requirement:
The UVI design (http://www.uvi.edu/sites/uvi/Pages/AES-Aquaculture-International_Aquaponics.aspx) or
aquaponic system actually removes a high proportion of the solid waste generated by the fish. This
is because solid fish waste can take time to break down and when it does break down, the process
often consumes oxygen. This means that the bacteria doing the solids break down (known as
mineralisation) actually compete with the fish in the system for oxygen. By removing solids, the UVI
approach lowers the competition for oxygen in the system so that the fish always have enough.
Many backyard and hobby scale aquaponic systems do not filter out the solid fish waste and these
generally end up in the media bed with the plants. As many people correctly suggest, the media bed
will act as a solid fish waste mineralisation filter and the fish wastes will break down or mineralise
over time. A flood & drain aquaponic media bed basically operates in the same way as a
Reciprocating Vertical Flow Wetland (RVFW), which also uses a flood & drain approach and has
very high treatment levels and can mineralise large amounts of solids. Therefore, aquaponic media
beds can and should be able to do the same. However, many RVFW’s are deeper than the standard Aquaponic media bed sizing calculator – USA Ver 2.0
5
300mm depth used for media aquaponic systems. So, often the surface area required for such a
shallow approach is larger than a standard RVFW. In addition, the top few cm’s of the bed surface
will always be the area of greatest oxygen content and therefore, will always perform the bulk of the
mineralisation. If we wish to use the media bed as a solids mineralisation site, then it also needs to
be sized so that there is enough surface area for the mineralisation bacteria to be able to efficiently
do their work.
The solid mineralisation bacteria we want to establish in the media are oxygen loving (aerobic) in
nature. Solids mineralisation will occur in deeper parts of media beds, however, often this is because
as the bed gets filled with more solid fish waste, the deeper parts of the bed can actually turn
anaerobic (ie: a lack of oxygen) and anaerobic mineralisation can occur. We must be very careful
with anaerobic zones entering aquaponic systems because these zones can release gases and
chemicals which may be toxic to the organisms living in the system, whether fish, plant or aerobic
bacteria. Therefore, it is recommended that anaerobic zones are not encouraged and aerobic
conditions are encouraged in aquaponic systems. This is why flood & drain water flow is
recommended, because the drain cycle helps to suck atmospheric oxygen deeper into the gravel
depth and allows more of the bed volume to act in an aerobic mineralisation mode.
The last important factor to understand in solids mineralisation capac
Aquaponic media bed sizing calculator – USA Ver 2.01Aquaponic Media Bed Sizing Model - USA Written by Wilson Lennard PhD Version 2.0, September 2012 Welcome to Version 2.0 of the Hobby Scale Aquaponic Media Bed Sizing Calculator. The calculator has been updated in a number of ways. The first change you will notice is that two of the outputs have been removed; the biofilter volume output and the bed surface area for fruiting plants output. The biofilter volume output has been removed because in all cases, when the media bed is sized for the fish feed to bed area ratio (based on the UVI ratio’s), the output gives a surface area that when using a 300mm deep media bed will always meet the biofiltration volume requirement. The fruiting plant bed surface area output has been removed because the original leafy green plant bed surface area is most often used, and if fruiting plants are to be grown, then the far lower planting density of fruiting plants (when compared to leafy greens) means that in the vast majority of cases, all things even out. The major upgrade to the calculator has been an improvement to the mathematics used to calculate the surface area of the bed required to mineralise the fish solid wastes. In the original version, due to the complex “log” based mathematics used, there was a “black hole” that appeared at lower fish densities which manifested as an inconsistency in the output whereby the surface area output could in some cases actually drop when the fish density rose. This has now been rectified and so no “black hole” should now be present in Version 2.0 and the bed surface area will rise as the fish density does. The other change is that there has been a slight “tweaking” of the UVI feed rate ratios. This is because I have gained more knowledge and insight into how much nutrient can be contributed by leaving solids in the system to mineralise and breakdown in the media bed. This current explanation document has also had several small changes done to it to reflect the changes in the calculator as outlined above. The major addition is a short discussion on how the addition of worms to the media bed MAY, or MAY NOT affect the media beds ability to breakdown and mineralise fish waste solids. I hope this calculator assists with your hobby scale aquaponic designing. Aquaponic media bed sizing calculator – USA Ver 2.02Introduction: Many backyard, hobby and domestic aquaponic system users, designers and builders are confused about the ratio between the fish tank size and the media bed size (gravel, Lecca etc…) in their systems. There are many “rule of thumb” approaches to this fish tank to media bed ratio, but these are not based on established scientific, technical or engineering principles. This document and the attached Spreadsheet calculator is an attempt to provide a useable method and model so that any hobby or domestic scale aquaponic system user or designer may have a guide to design and size their systems. This model and the outputs it produces are based on accepted and established scientific and engineering principles that are directly applicable to the design of aquaponic systems. Distribution of the Model: This model has been produced for FREE use by anyone who wishes to use it. It can be downloaded for FREE at www.aquaponic.com.au and other web sites. This means that the model can be effectively shared between users and you are welcome to distribute it, unaltered, at your discretion. The model and associated information (ie: how to use…) document is not to be sold by or to any person, organisation or party. The model has been produced and is available in both Metric and USA versions. All I ask is that if you use this model in a multi-user (ie: teaching classes or you are a system sales company) capacity, that you properly credit me as the writer and distributor of the documents. The Model: The Spreadsheet model that accompanies this document is a tool that allows you to size the area of the media bed in your system based on a number of important inputs. In addition, the model provides outputs for a number of parameters. Basically, the model will size the surface area of the media bed for you based on whether you wish for the bed to operate as a biofilter or as a solids mineralisation filter or as a plant growing component or a combination of all three. It is up to you, the user, to decide which bed size is best for your situation. However, it is recommended that the largest bed size given by the model will be the best for your system. Aquaponic media bed sizing calculator – USA Ver 2.03Component Ratio – plant growing area requirement: It is often thought that the ratio in aquaponic systems is between the fish tank volume and the plant grow-bed surface area or volume. However, this is not correct. The ratio is actually between the daily amount of fish feed that enters the system and the grow bed surface area. This is confirmed by the years of research conducted at the University of the Virgin Islands by Dr James Rakocy and his team which has ascertained a range of ratios for daily feed input to plant growing area for deep flow based aquaponic systems. The UVI ratios are: 1. For leafy greens – 0.20 oz/ ft2/day 2. For fruiting plants – 0.33 oz/ft2/day As can be clearly seen, plant growing area is directly linked with the daily fish feed input to the system. These ratios are also appropriate for media based backyard and hobby scale aquaponic systems, so the attached model allows you to size the grow bed area based on the plant growing area requirement as set by this UVI ratio. Aquaponic media bed sizing calculator – USA Ver 2.04The UVI model is based on fish that eat 32% protein feed (Tilapia spp.). However, many fish also used in aquaponic systems eat higher protein content feeds (45%). Therefore, the UVI ratio in the attached calculator has been re-calibrated for situations were high protein content fish feeds are chosen. In addition, most backyard and hobby aquaponic systems use the media bed as a place for mechanical filtration and mineralisation of solid fish wastes and this approach will supply extra nutrients to the system (the UVI system design removes the majority of the solids from the system very quickly). Because of this, the fish feed to plant growing area ratios have also been re-calibrated to take solids inclusion to the system into consideration when calculating plant growing area. Component Ratio – biofiltration requirement: The media bed in hobby and backyard scale aquaponic systems also acts as the primary location for biofiltration; the bacterial assisted conversion of potentially toxic fish waste ammonia to non-toxic nitrate. In actuality, the biofiltration requirement is not usually relevant to media based backyard and hobby scale aquaponic systems, because there is always an excess of media in the bed when the UVI ratios are followed and therefore, the biofiltration media volume requirement is always met. Component Ratio – solids mineralisation requirement: The UVI design (http://www.uvi.edu/sites/uvi/Pages/AES-Aquaculture-International_Aquaponics.aspx) or aquaponic system actually removes a high proportion of the solid waste generated by the fish. This is because solid fish waste can take time to break down and when it does break down, the process
often consumes oxygen. This means that the bacteria doing the solids break down (known as
mineralisation) actually compete with the fish in the system for oxygen. By removing solids, the UVI
approach lowers the competition for oxygen in the system so that the fish always have enough.
Many backyard and hobby scale aquaponic systems do not filter out the solid fish waste and these
generally end up in the media bed with the plants. As many people correctly suggest, the media bed
will act as a solid fish waste mineralisation filter and the fish wastes will break down or mineralise
over time. A flood & drain aquaponic media bed basically operates in the same way as a
Reciprocating Vertical Flow Wetland (RVFW), which also uses a flood & drain approach and has
very high treatment levels and can mineralise large amounts of solids. Therefore, aquaponic media
beds can and should be able to do the same. However, many RVFW’s are deeper than the standard Aquaponic media bed sizing calculator – USA Ver 2.0
5
300mm depth used for media aquaponic systems. So, often the surface area required for such a
shallow approach is larger than a standard RVFW. In addition, the top few cm’s of the bed surface
will always be the area of greatest oxygen content and therefore, will always perform the bulk of the
mineralisation. If we wish to use the media bed as a solids mineralisation site, then it also needs to
be sized so that there is enough surface area for the mineralisation bacteria to be able to efficiently
do their work.
The solid mineralisation bacteria we want to establish in the media are oxygen loving (aerobic) in
nature. Solids mineralisation will occur in deeper parts of media beds, however, often this is because
as the bed gets filled with more solid fish waste, the deeper parts of the bed can actually turn
anaerobic (ie: a lack of oxygen) and anaerobic mineralisation can occur. We must be very careful
with anaerobic zones entering aquaponic systems because these zones can release gases and
chemicals which may be toxic to the organisms living in the system, whether fish, plant or aerobic
bacteria. Therefore, it is recommended that anaerobic zones are not encouraged and aerobic
conditions are encouraged in aquaponic systems. This is why flood & drain water flow is
recommended, because the drain cycle helps to suck atmospheric oxygen deeper into the gravel
depth and allows more of the bed volume to act in an aerobic mineralisation mode.
The last important factor to understand in solids mineralisation capac
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