This is Chapter 7 of the Urban Aquaponics Manual.
In the last chapter, we developed a design specification for a small recirculating aquaculture system (RAS). Now. it’s time to select the components that we’ll need for the build.
Before we go too much further, I need to say that I don’t propose to provide a set of plans or a materials list for the design that we’ve produced. Just accommodating the measurement system differences from one country to another makes such an undertaking a nightmare.
Ultimately, you’ll make component choices based on…
- the amount of fish that you want/need to produce
- what’s available to you in the way of materials and equipment
- the amount of money that you have to spend
- your abilities and skills
- your personal preferences
…so, I believe that it’s more important that I provide you with options that can accommodate your specific circumstances.
We’ve all heard the old adage…”If you give a man a fish, you feed him for a day. If you teach a man to fish, you feed him for a lifetime.”
My goal, by the time you ingest the contents of this Manual, is that you should be able to take the principles that I describe and apply them to the broad question of system design rather than just be able to build one specific system.
Our goal is to produce clean, fresh food…so the materials from which our components are made – and any prior use that they may have had…must be safe for humans and fish. Reject any tank or vessel where you can’t be certain of what it contained before it became available to you.
At this stage, we’re just looking at components. While, for the purposes of illustration, I’ve approached the design process in a linear fashion, I recommend that you read the entire manual before you start to get too set on your design. Our basic design is just that…basic! There are plenty of things that we can do to enhance the basic design and I want you to have the opportunity to consider those tweaks and bells ‘n’ whistles before you finalise your plan.
That said, let’s commence our component search.
The key imperative of a fish tank is its ability to facilitate the removal of solid wastes.
Concentrating solids within reach of the drain is the consequence of tank shape and design…and managing water movement within the fish tank.
The ideal fish tank is robust, round in shape and will have a slightly sloping bottom with a centre drain at its lowest point.
Water returning to a round fish tank is directed tangentially at the surface. This creates a ‘hydrocyclone effect’ – setting up a slow circular movement in the water in the tank. A weak centrifugal force causes heavy matter in the water (solid wastes) to move outward to the wall of the tank and to slowly spiral down to its bottom eventually moving across the tank bottom toward the drain.
Most smaller purpose-built aquaculture tanks function like this.
They are also usually quite expensive. Secondhand units may become available but, you’ll need to act quickly since they are usually in high demand from aspiring small fish farmers.
Other off-the-shelf options (in order of preference) include:
- round plastic or fibreglass tanks with flat bottoms…like re-purposed rainwater tanks or large round livestock watering troughs.
- square plastic or fibreglass tanks…(preferably with rounded corners) like produce bins.
The desirable circular movement to which I referred earlier can be created in round tanks with flat bottoms – and even square tanks – and we’ll cover that in more detail as we get into the construction of our system.
Rectangular tanks are the most difficult to accommodate as fish tanks so I’d recommend that you avoid them if at all possible.
While I prefer those made of food-grade, high-density polyethylene or fibreglass, people have managed to repurpose all manner of containers for use as fish tanks.
DIY Fish Tanks
So long as we bear in mind the need to concentrate solid wastes so that they can be removed from the fish tank, the scope for viable do-it-yourself fish tank options is limited only by your imagination.
This situation is made possible by the existence of the food-grade low density polyethylene liner. LDPE liners are tough but flexible and can be used to line fish tanka that are built inground, on the ground and above ground.
They can be used in conjuction with existing concrete, steel/aluminium or brick/masonry structures – and you can build very serviceable fish tanks from timber and/or plywood and line them to make them waterproof.
Intermediate Bulk Containers
Notwithstanding that they are probably the most widely used off-the-shelf fish tank option in the world, I’m not a fan of IBC fish tanks – for the following reasons:
- Encouraging a circular flow in an IBC can be difficult and that can negatively impact solids removal.
- They are not fully UV-stabilised and will begin to fall apart over time.
- It’s hard to know what has been stored in them. They are often used as mixing tanks for herbicides and pesticides.
- They will always look like IBC’s.
Regardless of what I say, some of you will opt to use them anyway – so, if you’re certain about their previous use and they are really cheap, I’ll do what I can to help you to address their shortcomings later in the manual. We may even experiment with putting a bit of ‘lipstick on the pig’ to make it look a little less aesthetically confronting.
Mechanical and Biological Filters
I’ve built filters out of all manner of off-the-shelf and recycled containers. Some worked better than others. The ones that I liked the most just happened to be those that were the easiest to clean.
Not surprisingly, those that were usually the easiest to clean usually worked best…largely because a clean filter works better than a dirty one.
With the exception of swirl separators, which must be round, shape doesn’t matter too much. Having said that, I have a preference for round filter tanks mainly because they are readily available in a variety of sizes and they’re relatively inexpensive.
And, at the top of the list for cost and availability, is the ubiquitous recycled blue plastic barrel.
Indeed, the only drawback of these robust vessels is the colour. That can be addressed by buying new plastic barrels (available in a range of colours at four times the price of recycled ones) – or by cladding them in something a bit more aesthetically pleasing.
Water pumps are the means by which we recirculate the water through our RAS.
For our purposes, they tend to be of two main types – submersible pond pumps or externally mounted centrifugal pumps.
Pond pumps are cheap, very convenient to use, require minimal plumbing and are suitable for most urban aquaponics applications. The principal limitation of pond pumps is that they are best suited to low head applications. Flow rates will diminish quickly once the pumping head increases.
Externally-mounted pumps generally cost more to buy but usually move more water for a given power consumption – and they are better suited to applications where the water has to be pumped up heights of greater than a metre. Their installation is also a bit more complicated.
A Few Pump Hints and Tips
- Depending on your application, it may pay to consider using two small pumps rather than one larger one. The benefit of multiple pumps is that, if one pump fails, the other will keep your system going long enough for you to discover the problem. This is simple risk management.
- Avoid the use of submersible sump pumps – they are generally not rated for continuous operation – and they can be power-hungry.
- It may pay to buy more pumping capacity than you need initially – to cater for the likelihood that you’ll expand your system.
- While independence from the electricity grid is a worthwhile goal, solar-powered pumps add a new layer of complexity to the establishment of an urban aquaponics system. Keep it simple to start with. 240-volt (or 110-volt for US readers) pumps will provide for relatively reliable and inexpensive recirculation during your formative stages as an urban fish farmer.
Air Pumps or Blowers
I regard air pumps as essential equipment because low dissolved oxygen levels are the principal cause of fish deaths in small aquaponics systems. In any case, fish, plants and nitrifying bacteria all benefit from high dissolved oxygen levels.
In the event of water pump failure, good supplementary aeration may be the difference between a minor nuisance and a disaster. Air pumps are cheap insurance.
Our little system is going to require aeration at several points:
- Fish tank – continuous
- Moving bed biofilter – continuous
- Packed media filter – periodic…when cleaning
- Plant growing system – continuous
We can have one larger air pump that meets all of these requirements – or we can have two (or more) air pumps to deal with specific parts of the system. Air pumps (particularly those with diaphragms) can fail at short notice so having a couple of smaller air pumps might be a useful risk management strategy.
Pipe and Fittings
PVC pipe in the range of 25mm – 50mm (1″ – 2″) is widely used for backyard fish farming and is easy to work with. PVC pipe and fittings in our preferred size range are of two main types…pressure and drainage. The types are not compatible with each other although experimentation (and the judicious application of heat) will enable you to reconcile the types where circumstances demand it.
We’ll be using 25mm (1″) PVC pressure pipe and fittings for the water supply side of our little system and 50mm (2″) for all drainage pipework.
Some people like to use larger stormwater pipes and fittings on the drainage side but I’ve found that the lower water velocity of 90mm+ pipework often allows solids to settle out in the pipes – with the potential to create anaerobic zones.
Control valves may be required in some situations and the two most common types in use are ball valves and slide valves. Ball valves are available from the same places that stock the PVC pipe and fittings. Slide valves are nicer to use, more expensive to buy and are usually only available from specialty aquarium/aquaculture suppliers.
Connecting Tanks and Pipes
Secure connections of pipes to tanks are achieved through the use of bulkhead fittings (also known as tank outlets) Uniseals and flange fittings. Each of these has their place in RAS construction and we’ll learn more about them in the next chapter as we begin the build.
One of the challenges with this chapter, was deciding what to leave out (rather than what to include). The list of gadgets that can be included in a small-scale RAS is long. What we’ve covered here will allow you to build a RAS that is productive, resilient and versatile. You can always reflect on the available bells ‘n’ whistles later – as you sit down to eat your first fish and salads.
In the meantime, I propose to build our little 1,000 litre system using the following:
- IBC – not because I like them but because (regardless of what I say) some of you are going to use them.
- Blue barrels – I’ll use three of them to create a radial flow filter, a packed media filter and a moving bed biofilter.
- PVC pipe and fittings – we’ll use 25mm (1″) for the pressure pipework and 50mm (2″) for the drainage.
- Pump – 4500 litre submersible pond pump.
- Bulkhead fittings, Uniseals and flange fittings – to hook it all together.
In the meantime, I invite you to comment…to express any concerns that you may have…and to provide ideas or suggestions that you feel will improve the book – or add value to it.