Bio-filters, Microbes, Stands & More
Once again, welcome back to my twice-monthly DigiLetter, 'Aquaponics: The Definitive Reference'.
Recapping on my previous issues, by now you should have a good idea of where you want your aquaponics system located and what size it will be. You should know what type of grow-media you will be using – scoria/pumice/lava rock, expanded clay balls, gravel etc. – and where that grow-media can be sourced (not to mention how you will initially wash the media, prior to use). You know that appropriately sized, food-safe tanks for the fish and the grow-beds – such as HDPE rainwater tanks – need to located and acquired. I have covered the relative size ratios required of these vessels and I have also covered some of the basics of how they should be arranged and plumbed. So, what's next?
Stands
The grow-beds need to be raised quite a way to achieve a good water depth in the fish tank and one cannot stress enough the importance of strong and stable grow-bed stands. Since 1 litre of water equates to approximately 1 kilogram, grow-beds can be extremely heavy and as a result they are always going to be top-heavy. Besser blocks, concrete blocks, bricks, steel or thick timber are suitable materials to build stands for grow-beds.
The
above image is a 600 litre grow-bed and stand, built by the author.
This was a successful experiment in using thick HDPE liner, folded to
shape and supported by the wooden frame as a grow-bed. Otherwise it was
plumbed normally.
Earthworks are a solid solution for supporting grow-beds in large or commercial systems, at least for those with access to the machinery and know-how. For systems where aesthetics is an important element, 25mm extruded aluminium square tubing and associated fittings can be customised in a grid/matrix fashion to support unlimited grow-bed sizes, just by keeping all tube lengths to 450mm or less. With a suitable geometric layout of the beds and tanks, this can look quite striking when supporting a colour-coded rainwater tank aquaponic system especially after everything has been cut, customised and edged with black rubber tubing. Now, imagine it overflowing with plants and produce! Aquaponics doesn't have to be patched together out of recycled and second-hand goods. In fact, if you want it to last for decades and therefore appreciably contribute towards solving our global environmental problems, then it is definitely best to purchase new. Nothing will last like modern poly water tanks.
The maximum water depth of your fish tank is determined by the distance from the bottom of the fish tank up to the bottom of the grow-beds. This should be somewhere between 450mm and 1200mm, depending on the shape of the vessels and the desired fish tank volume. Any deeper and the bottom of the tank cannot be reached from the outside with a net, not to mention that the energy cost to push water up that high begins to add up (pump 'head'). This can become a problem down the track when expanding the system and trying to transfer over to a limited source of renewable energy. Furthermore, water depths over 1200mm mean the grow-beds end up being above a comfortable height for working on (that being somewhere between hip and chest height). Any shallower and managing water temperature becomes near impossible – not to mention the issue of going back to gardening on your knees! Personally, I prefer my fish tanks at just over 1 metre deep, maximum. Burying or recessing the fish tank into the ground is also a way to obtain good water depth without having to construct grow-bed stands that are too high and too unstable. Positioning the fish tank next to a retaining wall, verandah or other raised platform also allows for shorter and more stable grow-bed stands by having them on top of the raised platform.
Earthworks are a solid solution for supporting grow-beds in large or commercial systems, at least for those with access to the machinery and know-how. For systems where aesthetics is an important element, 25mm extruded aluminium square tubing and associated fittings can be customised in a grid/matrix fashion to support unlimited grow-bed sizes, just by keeping all tube lengths to 450mm or less. With a suitable geometric layout of the beds and tanks, this can look quite striking when supporting a colour-coded rainwater tank aquaponic system especially after everything has been cut, customised and edged with black rubber tubing. Now, imagine it overflowing with plants and produce! Aquaponics doesn't have to be patched together out of recycled and second-hand goods. In fact, if you want it to last for decades and therefore appreciably contribute towards solving our global environmental problems, then it is definitely best to purchase new. Nothing will last like modern poly water tanks.
The maximum water depth of your fish tank is determined by the distance from the bottom of the fish tank up to the bottom of the grow-beds. This should be somewhere between 450mm and 1200mm, depending on the shape of the vessels and the desired fish tank volume. Any deeper and the bottom of the tank cannot be reached from the outside with a net, not to mention that the energy cost to push water up that high begins to add up (pump 'head'). This can become a problem down the track when expanding the system and trying to transfer over to a limited source of renewable energy. Furthermore, water depths over 1200mm mean the grow-beds end up being above a comfortable height for working on (that being somewhere between hip and chest height). Any shallower and managing water temperature becomes near impossible – not to mention the issue of going back to gardening on your knees! Personally, I prefer my fish tanks at just over 1 metre deep, maximum. Burying or recessing the fish tank into the ground is also a way to obtain good water depth without having to construct grow-bed stands that are too high and too unstable. Positioning the fish tank next to a retaining wall, verandah or other raised platform also allows for shorter and more stable grow-bed stands by having them on top of the raised platform.
Bio-filters
As discussed in the first issue, aquaponics
is entirely powered by microbes – specifically, various species of
bacteria and archaea. These are commonly referred to as AOMs –
ammonia-oxidizing microbes. Sometimes they are also referred to as
chemolithoautotrophs, however the only reason I mention that is simply
to say chemolithoautotrophs. Wow.
Being such tiny organisms, they can (and will) inhabit every dark and damp nook-and-cranny in your aquaponic system – and the more the merrier. Indeed, this is the primary reason for the choice of flood-and-drain grow-beds in aquaponic systems. The deep media-filled beds provide just the habitat the AOMs are after, with plenty of surface area on the medium to colonise. While AOMs will be found throughout the water column and their generous population should change the water colour to a slight tanin-brown, they are not really 'working' at their best while submerged in open water. To be truly happy and efficient, they require a surface to attach to. Furthermore, water cannot provide enough oxygen for them to efficiently oxidise ammonia. No matter how hard you try, water has a maximum limit to its oxygen-carrying capacity and this is not a sufficient concentration for efficient ammonia-oxidation by these little helpers. Roaming AOMs and slight water colouration are just side-effects of having a healthy system with a large population.
Being such tiny organisms, they can (and will) inhabit every dark and damp nook-and-cranny in your aquaponic system – and the more the merrier. Indeed, this is the primary reason for the choice of flood-and-drain grow-beds in aquaponic systems. The deep media-filled beds provide just the habitat the AOMs are after, with plenty of surface area on the medium to colonise. While AOMs will be found throughout the water column and their generous population should change the water colour to a slight tanin-brown, they are not really 'working' at their best while submerged in open water. To be truly happy and efficient, they require a surface to attach to. Furthermore, water cannot provide enough oxygen for them to efficiently oxidise ammonia. No matter how hard you try, water has a maximum limit to its oxygen-carrying capacity and this is not a sufficient concentration for efficient ammonia-oxidation by these little helpers. Roaming AOMs and slight water colouration are just side-effects of having a healthy system with a large population.
