This is Chapter 5 of the Urban Aquaponics Manual.

In previous chapters, we looked at what recirculating aquaculture is – and how it works in a basic microbiological sense.  Most importantly, we should have connected with the fundamental notion that aquaponics starts with a recirculating aquaculture system.

Before we leap into the design and construction of a RAS, however, let’s take the opportunity to consider a few things that will impact your system design.  

Don’t allow these considerations to overwhelm you.  Just have them in the back of your mind as you sit down to plan your system.

Up until now, we’ve been talking about recirculating aquaculture systems.   The considerations in this chapter apply equally to the RAS – and its attached growing systems.

Health and Safety

My inclusion of Health and Safety at the top of this list is deliberate.

Every day, we hear of people who have been killed or seriously injured in so-called freak accidents.  In truth, however, there’s usually nothing accidental about health and safety incidents (as they are more appropriately called)  around aquaponics systems.  They are are almost always preventable.

The health and safety risks that apply to aquaponics systems include:

  • Drowning
  • Electrocution
  • Poisoning
  • Manual Handling 
  • Structural Collapse

A fish tank is no less dangerous than a swimming pool or a spa. How will you ensure that small children cannot climb into your fish tank? The ideal is to cover the tank but the least that should happen is that you should be able to exclude children and pets from the area.

Electricity is an essential part of any aquaponics system but it does not suffer fools lightly.   Think carefully about how you will manage prospective electrical hazards.

To prevent your family from ingesting toxic substances, or to avoid poisoning your fish, you should ensure that your system components are made from safe, inert food-grade materials.

If you are contemplating the use of recycled materials, you need to confirm that they have not previously been used to contain toxic substances.

Manual handling is another issue that requires careful consideration, too. There’s no shortage of heavy things to lift and a hernia or a dislocated disc are a high price to pay for a momentary manual indiscretion.

Manual handling injuries are not the only weight issues. A 200-litre (55 gallons) drum of water weighs around 200kg. A 1,000 litre (250 gallons) weighs a metric ton. Given the potential for injury to people (and damage to property), there’s no place for sloppy construction.

Environmental Control

Fish and plants (like everything else) grow best in a particular environment.  While that environment will include water quality, dissolved oxygen levels and pH, our main environmental concern (for design purposes) is temperature.  Our secondary concern, specifically for plants, is light.

Temperature will impact your choice of fish species and the types of plants you can grow – and when you can grow them.  The amount of natural light that is available to you will also directly impact plant production.

You can control the environment in which your fish and plants grow.   Indeed, you can keep warmwater fish species in the depths of a Montana winter.  As a general principle, however, the further away from the optimal temperature range that you get for your preferred fish species, the more money you are going to have to spend to heat their water.

Similarly, you can grow plants in a basement or warehouse that never sees sunlight but providing artificial lighting of the correct photoperiod, intensity and spectrum is going to require significant investment.

Points of Failure

A recirculating aquaculture system is a life support system.  

If it stops functioning, for whatever reason, the living organisms that it supports will die.  An aquaponics system may experience catastrophic failure for a variety of reasons including:

  • Power interruptions
  • Equipment failure
  • Serious leaks or bursts

So, when sitting down to design your system, you need to undertake a bit of ‘what if’ analysis.

What if the power supply is interrupted? What if the pump(s) seize? What if you experience unseasonal rainfall, wind or extremes of hot or cold? What if you had to leave your system unattended for a day – or a week?

Think of every piece of pipework…and every fitting…as a prospective point of failure and design your system accordingly.

System Scale

If your system is to be housed in an urban backyard it will need to be reconciled with other backyard activities including entertaining, play area or pet space.

Sustainability

Herbicides, pesticides and chemicals will kill your fish and have no place near an aquaponics system.  The planet is well overdue for a respite from its most troublesome organism…humans…so cut it a break and use  materials that have the lowest possible environmental impact or those that can, at least, be fully recycled.

Durability

Your choice of system components should take account of their lifespan.

Cost Effectiveness

A key question when making any investment is “How quickly do I get a return on my investment?”  Your system design should provide you with clean, fresh food without breaking the bank.

Once the system has been built, it will cost money to operate.  Your biggest variable operating expense is the energy required to run the water and air pumps – and to heat/cool the water in the water in the fish tank – and your system should be designed to minimise these costs.

Portability

The ability to empty a system and to relocate it is a distinct benefit for people who rent accommodation. The system will also retain its resale value if it can be moved relatively easily.  Consider the use of rubber slip joints and barrel unions to enable you to dismantle and re-assemble the components as needed.  Similarly, consider quick release couplings for water hoses, air lines and electrical/data connections. 

Your choice of plant growing systems is particularly important if you need portability.  

Accessibility

Having tanks and growing systems at a comfortable working height is an issue for everyone but particularly for people with disabilities.  Can you overcome space limitations (with a small system) by mounting some components on robust castors? 

Ease of Operation

Your filters will require regular cleaning.  Do you have drains at the lowest points in the system to ensure that there are no places for water and organic matter to be trapped and become anaerobic?

Are thermometers and digital displays located so that they are easy to read?

Aesthetics

Whether you get to engage in food production may require that you satisfy your partner that you are not going to create an eyesore in your backyard.

Similarly, your neighbours may begin to take an unhealthy interest in your system if they perceive that their property values are negatively impacted by your activities.

You may argue that what you do in your own backyard is your business but local government authorities will take a different view if they start receiving complaints from disaffected neighbours.

A neat and tidy system is also easier to operate and keep clean.

Nuisance Potential

Nothing will bring the wrath of the local health inspector down on your head faster that something that stinks or attracts vermin.

Still water is a breeding haven for mosquitoes and, if it contains nutrients, it can become anaerobic and will quickly produce bad odours.

Managing your system in a healthy state is essential.

System Location

Whirring pumps and running water might be music to your ears but could well drive a neighbouring shift worker to distraction. Locating your system out of hearing range will avoid this issue.

What are the other design implications of your preferred location?  Does your proposed plant growing area have enough sun?   Or too much?  Is your fish tank going to be located inside our outside? If outside, what is the likely effect of sun, wind and rain on your fish tank?  What is your closest access point to power and water?

The system design should also integrate well with other food production units.  You may decide to extend your backyard self-sufficiency endeavours to include laying chickens, meat chickens, fruit and nut trees, quail, rabbits, worms and other possible integrations. You should design your system with this in mind.

Size Does Matter – and Small is Beautiful

This implied contradiction simply suggests that choosing the optimum tank size is a question of balance – too small and you’ll become a slave to the system – too large and you’ll chew up too many resources while trying to achieve a useful result.

For backyard purposes, I suggest that your first tank be of 800 to 2000 litres (200 to 500 US gallons). A system of this size will allow you to produce 15 – 50kg (30 – 100lbs) of fish per year without the need for you to become its constant companion as you juggle the production parameters.

For the purposes of this discussion, this is a small system…not to be confused with the micro ‘demonstration of concept’ units that people sometimes build in their homes.

You can always increase the size of your system once you satisfy yourself that aquaponics is really for you and once you’ve had the opportunity to educate yourself properly about some of the options that are available to you.

In any case, if you can’t operate a small system, you won’t be able to operate a large one.

Even if you are planning a larger system, having two or more 1000 litre tanks makes more sense (particularly in an urban aquaponics context) than having one large tank. You can keep fish of different species and ages and managing risk is easier if you have several smaller tanks.   Losing some of your fish might be annoying but losing all of them would be a tragedy.

Smaller tanks are also easier to move about and cheaper to cover and insulate.

You may be thinking, by now, that designing an aquaponics system is much more complex than you previously realised.   The truth of it, however, is that it’s much simpler than it sounds.

In the next chapter, I’ll show you the process that I use to design a small recirculating aquaculture system.

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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.