In a recent post, Aquaponic Gardening blogger Sylvia Bernstein ponders the question…. “How deep should your aquaponics grow bed be?”

Suggesting that grow bed depth is the subject of some controversy, she quietly acknowledges that shallow grow beds are lighter…..and cheaper to purchase and fill with media.

Ms Bernstein then reveals herself as an apologist for the mythconception movement as she argues (unconvincingly) the case for 300mm (12”) grow beds.

Her case hinges on the same hoary old chestnuts about “limitations on the types of plants that you can grow” and “dead zones” that will require the bed to be cleaned.

While it’s easy to dispute these feeble attempts to twist logic (see here), the one that really got me was the suggestion that 12” grow beds should be used because such self-illuminati as Joel Malcolm, Murray Hallam and she (I sense another AP “expert” about to emerge here) “all talk about the limitless range of plants that can be grown” because “we are all using beds about 12” deep.”

Now, wide acceptance of an idea is not proof of its validity; much less a decree by a small group of individuals who are so clearly confused about how backyard food production really works.

At the heart of the nonsense about grow bed depth (and other mythconceptions about stocking densities, component ratios and solids removal) is the flawed translation of the Speraneo flood and drain aquaponics model.

Of course, aside from perpetuating mythconceptions the other thing that this trio have in common is that they all sell grow beds.

While aquaponicists are quite used to seeing expensive plastic and fibreglass grow beds, Ms Bernstein’s AquaBundance units are breaking new ground at over AUD$40.00 per square foot.

Of course, it should be remembered that, although she is a relative newcomer to hawking aquaponics kits, as a former R&D executive for the folks who made the Aerogarden, she’s certainly no stranger to high-priced backyard food production real estate.

While she attaches to what she describes as principals (sic), telling people that they should (or must as Hallam states) do something which is so obviously lacking in logic, leaves one in little doubt about whose interest is really being catered to.

As it is, most of the plants that Sylvia says favour deeper grow beds are best grown using other (much less expensive) growing options like satellite posts or wicking beds.

The fact is that when it comes to growing fish and plants, you can use grow beds of any depth……or not at all.

-o0o-

Aquaponics is demonstrably a great way to produce clean fresh food.

Like any good idea, however, aquaponics has attracted its fair share of opportunists and false prophets.  Simplistic guidelines and exaggerated performance claims have resulted in many system failures.

The fact is that keeping fish is the same as keeping any other type of livestock – it comes with responsibilities.

They need to be stocked at appropriate levels, fed properly and provided with appropriate accommodation.  They need to be checked at regular intervals and their quarters kept clean.

Failure to undertake these responsibilities around any livestock will (at best) result in lost productivity and (at worst) in diseased or dead stock.

For most of the past four years, we’ve run several small aquaponics systems simultaneously.  We’ve trialled different configurations, species and age groups.

Our experience confirms the following:

• It is not useful to make generalised stipulations around stocking rates because of the variables involved.
• With smaller systems, things happen faster…..for better or for worse.
• An aquaponics system that is equipped with effective mechanical and biological filtration will produce more fish in greater safety than any basic fish tank/grow bed model of an equivalent size.
• The only sure way to be certain that a system is in good health is to test the water – and manage the unit according to the results – on a daily basis.

At the popularly touted 2:1 (grow bed volume to fish tank volume) ratio, it is unlikely that even the frequently recommended 20 – 30kg (per 1,000 litres) stocking density, may be sustainable for some species.

Remember, these stocking densities were originally premised upon tilapia – a very tough species known for their ability to survive in water of indifferent quality.

For some species, the stocking density is much less….something in the order of 5 – 10kg per 1000 litres of water.

When I first suggested that simplistic guidelines and exaggerated stocking rates were largely responsible for the daily procession of fishkill stories on aquaponics forums, I was greeted with howls of protest.

Over time, however, we demonstrated that the ‘one size fits all’ approach to aquaponics wasn’t going to work for many people and a new rationalisation began to emerge.

Some of our critics began to recall how their systems functioned best when very lightly stocked.   To support their contention about low stocking densities, they began to speak about how, since aquaponics was really more about plants than fish anyway, low stocking rates were really the way to go.

While it was useful that these people began to acknowledge that the standard aquaponics system had stocking limitations, this position ignored the fact that it cost the same amount of money (in terms of component costs) to house ten fish in 1,000 litres of water as it does to house 50.

It also costs the same amount of money to pump water for 10 fish in a tank as it does for 50 fish in a similar quantity of water.

Fish production is not the only issue. Fifty fish will support many more plants than ten fish.

What these folks failed to grasp was that throttling the system was not the only option.  What we (and others) proved is that, through changes to system design and operation, you can improve the productivity and resilience of the standard flood and drain aquaponics system.

If you are going to maximise the return on your investment in system components, energy and time, you need to grow the maximum weight of fish and plants in the shortest possible amount of time.

The alternative is to waste money, energy and time.

The good news is that you can enhance your existing aquaponics system (without spending a cent) by:

• Ignoring simplistic guidelines – they’ve got us to where we are now – a mounting tally of dead fish stories.
• Matching the stocking density to the nitrification and aeration capabilities of the system…and the only way that you can do that is through….
• Testing water quality…..very regularly!  Forget the nonsense about “sniffing the water” (a recommended alternative to testing from one “guru”) – you can’t detect low oxygen levels (the principal cause of fish deaths) by nose.
• Manage your system according to your water quality test results……and take appropriate action…..immediately!   Don’t wait until tomorrow to address low oxygen or rising ammonia/nitrite levels – you’ll only need a convergence of other things like hot weather, an algae bloom or overfeeding…….to push abnormal levels to fatal ones.

Anecdotal evidence from many other people supported our own observations that the most productive aquaponics units were those that were subject to rigorous testing and maintenance routines.

In the best managed systems, things can still go wrong and it’s how you handle those situations that will largely determine whether you’ll get to cook and eat your fish or cry over them at their wake.

When your test results evidence a current or looming water quality issue:

• Stop feeding
• Check your tank bottom for uneaten food and remove it.
• Increase the flow rate through your system – more water flow means more nitrification and aeration.
• Add salt – at the rate of 1 – 2 parts per thousand.  That’s 1 – 2kg of salt to each 1,000 litres of water.
• Boost aeration – there are very few water quality issues that will not benefit from more oxygen.
• Change water – if things are not moving quickly in a positive direction.  This might be seen in some quarters as wasting water (that depends entirely on what you do with it next) but having your fish die for the want of a water change is just plain dumb.  Limit your water change to that needed to address the problem.

These things amount to a rite of passage rather than a real passport to productivity – they’re things that you must do just to stay in the game – and they apply to any aquaponics system.

Other useful ideas include:

• Placing an orphan sock over the inflow pipe and  rest this on a piece of filter foam  This will trap much of the sedimentary solids and some of the suspended solids…..and takes just a few seconds each day to rinse out.
• Placing a handful of composting worms in the system bio-filter. They will not only assist the mineralisation of those solids that do make it into your grow beds but they’ll also reduce their volume.
• Set your grow beds up so that they can be cleaned easily.  We use clay pebbles in our beds and, where practical, we limit their depth to 150mm.  This makes cleaning our grow beds as easy as dragging our hands through the media to trap the roots from recently harvested plants.  We periodically flood the beds up and stir up the media while draining the watery solids onto our soil-based gardens.
• If your fish tank is such that uneaten food or solid waste accumulates on the tank bottom, remove it on a daily basis…..before it begins to putrefy and generate ammonia.

These few simple strategies will extend the productivity and resilience of your aquaponics system…..and they’ll cost you nothing but a bit of time.

To summarise, keeping any form of livestock comes with daily responsibilities and fish are no different.  Spending a few minutes each day on water testing and making appropriate adjustments to your system will allow you to optimise the return on your investment of time, energy, money and effort.

While this may be a disappointment if you purchased your system on the premise that all you had to do was add water and fish, reconcile yourself to the fact that empathising with other aquaponicists about fish kills is much easier than standing in their midst.

In my next post, we’ll show you how to re-configure your aquaponics system for even greater productivity and resilience.

-o0o-

Most commercial aquaponics units are raft systems.

This is largely due to the long standing influence of the UVI Aquaponics Research Center, and the success of their model.

Raft systems are somewhat under represented at the backyard level – particularly in Australia – probably due to early promotion of the Speraneo-style flood and drain model.

The Raft System

Raft aquaponics is essentially the same as the CHOP system but, instead of media-based flood and drain grow beds, raft tanks or troughs are used to grow plants.

The other essential difference is that raft systems invariably feature mechanical filtration.  Even aquaponics fundamentalists, who might argue (albeit unconvincingly) that particulate waste can remain in a flood and drain system, acknowledge the need for mechanical filtration in raft systems.

For practical purposes, water flows from the fish tanks through filters and into grow tanks or troughs which contain Styrofoam rafts.  The rafts support the plants.

The water flows from the grow tanks into a sump tank.  A pump located in the sump tank moves the water back to the fish tank.

The water in the raft system recirculates continuously.

The Aquaponics Research Centre located at the University of Virgin Islands (which has been operating for over 25 years) is arguably the most widely recognised aquaponics system in the world and serves as the model for most raft systems.

The advantages of the raft system include:

• Its stability – the relative volume of water in a raft system ensures that it is more stable (in terms of water quality and temperature) than flood and drain systems of a comparable size.
• Easier to operate – little testing required and minimal daily maintenance.
• The existence of a large body of research data.
• Cheaper to build than flood and drain systems of comparable size – small sump tank.
• Higher productivity than flood and drain systems of a comparable growing surface area.
• Portability – small backyard systems can be emptied and moved relatively easily.

Raft tanks can be built from timber, plywood, cement blocks, pre-cast concrete sections, fibreglass or (for smaller systems) plastic.

The plants are inserted into holes cut into the Styrofoam rafts.  The hole spacing will vary according to the type of plant to be grown.

Raft systems are ideal for the production of Asian greens, salad leaf vegetables and soft herbs, however, they have also been used to grow many other vegetables – particularly tomatoes.

It’s likely that raft aquaponics will become more common at the backyard level as people become better educated about its benefits.

-o0o-

The deficiencies of the aquaponics Sump Tank System were alleviated by the (re)discovery of the CHOP System.

CHOP is an acronym for Constant Height/One Pump. In some parts, the CHOP system will be known by the more vulgar acronym CHIFT PIST (constant height in fish tank – pump in sump tank).

The CHOP system is a variation on the single pump system used by the UVI Aquaponics Research Centre.  Where the UVI model employs the raft growing system, the CHOP system is adapted for use with grow beds.

With the CHOP system, the water flows from the fish tank to the media-based grow beds before draining into a sump tank.  A single pump in the sump tank then pumps the water back into the fish tank.

The CHOP System

Importantly, the level in the fish tank remains constant because the only water that leaves the fish tank is that displaced by water being pumped up from the sump tank.

If you should develop a serious leak outside of the fish tank, the pump in the sump tank will eventually stop (because there is no more water flowing back into the sump tank) but your fish tank will remain full.  This eliminates a prospective point of failure.

While grow beds usually flood and drain at different times, the sump tank has to be large enough to accommodate the reality that (sooner or later) the grow beds will all fill at the same time.

For design purposes, a media-filled grow bed will contain 30 – 40% of the media volume in water.  For example, a 600 litre grow bed will contain 200 – 240 litres of water – assuming that it is filled to capacity with gravel or clay pebbles.

If we have four 600litre grow beds (each having a water capacity of around 200 litres of water), a sump with a capacity of around 1,000 litres will be required.

The good news is that, although a larger sump tank will be required, it can be set up in such a way that it can serve multiple purposes……including an ebb and flow water garden or a Moving Bed bio-filter.

The advantages of the CHOP system include:

• Flexibility in placement of the grow beds.
• Only one pump required – energy savings.
• No need for timers or float switches.
• No pump in the fish tank – avoids churning solids up.
• You can network two or more fish tanks so that nutrient levels remain constant right across the system.
• You can use a single mechanical and biological filtration system to serve several fish tanks.
• Water level in the fish tank remains at a constant level.
• Water tank remains full in the event of plumbing or equipment failure.

The disadvantages include:

• More expensive to set up than a basic flood and drain unit.
• Requirement for a larger sump tank – equal to the total volume of water able to be simultaneously contained in the grow beds.

A much smaller sump can be used if continuous flow watering (surface or sub-surface) is used in place of the usual flood and drain watering regime.

If you choose this option, I recommend that you incorporate a trickling bio-filter into the design to optimise nitrification and aeration.

The CHOP System has become the layout of choice for the more serious flood and drain aquaponicist……for the benefits that it offers.

-o0o-

The Sump Tank System was popularised by Missouri farmer (and aquaponics pioneer) Tom Speraneo.

It made its way to Australia in the mid 2000’s when Western Australian Joel Malcolm mirrored the Speraneo system.

In its most basic configuration, the Sump Tank System comprises a fish tank, two pumps, float switches and timer (or auto-syphons) and grow bed(s).

A pump (located in the fish tank) moves water to the grow beds which fill up and eventually drain into a sump tank.  The flood and drain action is controlled by a timer or auto-syphons.

A float valve in the sump triggers a second pump once the water rises to a particular level and moves the water back up to the grow beds.  Once the water level in the sump tank drops sufficiently, the float switch turns the pump off.

The Sump Tank System

The only real benefit in using the Sump Tank System is that it offers greater flexibility in the placement of grow beds than does the basic flood and drain system.

The disadvantages include:

• Fluctuating fish tank levels.
• Greater complexity.
• More expensive to set up and operate.
• More prospective points of failure.

The Sump Tank System is something of a relic these days and has been made redundant by the emergence of the CHOP (constant height/one pump) system…..the subject of my next post.

-o0o-

The microFish Farm is a small recirculating aquaculture system (with a capacity of 600 to 1200 litres) characterised by a square fish tank and an overhead bio-filter.

The microFish Farm

It earns its place in our list of system layouts because it has been replicated many hundreds of times throughout Australia.

When we first developed the microFish Farm concept, several years ago, it was innovative for a number of reasons including:

• It was the first turnkey backyard-scale aquaponics system in Australia.
• It featured vertical stacking of components.  The bio-filters were located on top of the tank which avoided the need for a support frame.
• Its compact footprint and efficient use of space.
• Its ability to be used inside or outside.  In its second incarnation, it featured a long rectangular bio-filter that could also be used as a grow bed.
• It demonstrated that useful quantities of freshwater fish could be grown in as little as 600 litres of water.
• Its use of an access barrier – to keep toddlers, sunlight and predators out…..and the fish in.
• Its simplicity.
• Its capacity to be used in conjunction with a wide range of hydroponic and soil-based growing systems.
• Its ability to be disconnected from the growing system in the event of disease or infestation in fish or plants……or to minimise overnight heat loss.

Square tanks offer efficient use of space

A small submersible pump raises the water from the fish tank to an overhead flood and drain bio-filter.  When the water level reaches a certain point an autosyphon is triggered unleashing a torrent of water back into the fish tank.

Our first microFish Farms were built from off-the-shelf components.  We used 780 litre HDPE plastic bins (made for the horticulture industry to transport fruit and vegetables) as fish tanks.  Recycled plastic barrels or stacking plastic crates (filled with oyster shells) were used for trickling bio-filters.

Fibreglass variants of the microFish Farm are also offered by two Australian manufacturers.

The fibreglass variant of the microFish Farm

Where the movement of  water through the overhead bio-filter is controlled by an auto-syphon there will be modest fluctation in the fish tank water level.

The microFish Farm can also be set up for continuous flow.  Under this regime, the water level in the fish tank does not fluctuate.

If located outside, the overhead bio-filter can be planted out with seedlings, at which point the microFish Farm becomes a small aquaponics system.

A variety of other hydroponic growing systems can be added to the system – or the water from the fish tank can be used to irrigate soil-based food gardens.

Our 4 Tank system comprised (not surprisingly) four microFish Farms alongside of each other and provided the opportunity to trial different species and age groups.

The 4 Tank System - clean fresh food just eight feet from our back door.

While it suffers from some of the same limitations as other conventional aquaponics systems, the microFish Farm is both innovative and versatile.

Well managed, it is capable of producing plenty of clean fresh food.

-o0o-

The basic flood & drain aquaponics system is the most common system layout.  

There are probably thousands of them in use throughout the world and most of them (to a greater or lesser extent) produce fish and plants.

The system comprises a fish tank, a submersible pond pump and one (or more) flood and drain grow bed(s).

The grow beds are positioned in such a way that they drain directly back into the fish tank and the flood and drain cycle is controlled by a timer or an auto-syphon.

The most common aquaponics system layout.

 The pump, which is located in the fish tank, lifts water into the grow bed(s).  Once the water reaches a pre-determined level, the pump will stop (or the auto-syphon will start) and the grow bed(s) will drain back into the fish tank.

The advantages of the Basic Flood and Drain layout include:

• Its simplicity
• It’s cost effectiveness

The disadvantages of this layout include:

• The need to provide support stands (and/or to partially bury the fish tank) in order to place the grow bed(s) above the top of the fish tank.
• The number of grow beds limited by the available fish tank volume (without resorting to spider valves and other expensive solutions).
• Fluctuating water level in fish tank.

Other Points:

• Raft tanks can be used in conjunction with (or in place of) grow beds.
• Continuous flow watering of the grow bed can be used in place of flood and drain irrigation.
• The advantage of continuous flow watering, or raft tanks, is that you do not experience the fluctuating fish tank water levels that you do with flood and drain grow beds.
• Where you elect to use raft tanks or flood and drain media-based grow beds, it is advisable to attach a trickling bio-filter to the system to underpin nitrification and to enhance aeration.  While this is advisable for all aquaponics systems it is particularly applicable to small ones.
• Without mechanical filtration, this layout (as with all aquaponics systems) will be limited in terms of stocking density and nutrient production.

In 2007, we designed the microFish Farm (a variant of the basic flood and drain design) which is the subject of my next post.

-o0o-

People who are new to aquaponics often struggle with the matter of system layout so I thought it timely to list the various layouts and describe how they work.

While there are various ways to skin the aquaponics cat, the main layouts include:

1. Basic Flood and Drain
2. The microFish Farm
3. The Sump Tank System
4. CHOP – Constant Height One Pump

Each of the layouts has its own advantages (and some disadvantages).  Within these basic categories, there are lots of variations on the aquaponics theme and aquaponicists (being the innovative souls that they are) have developed lots of interesting ideas to enhance the performance of their systems.

Since many people who aspire to build their own aquaponics systems have a limited budget, it’s important to be able to build what you can afford first and then enhance it as resources become available.  It’s useful, therefore, to factor prospective change into your design.

I’ll be back in a day or two with my next post….on the Basic Flood and Drain system.

-o0o-

Are aquaponics kits a rip off?

This is the question posed by TreeHugger’s Sami Grover in response to Hawaii-based Friendly Aquaponics’ announcement that they had produced plans and operating manual for a micro-aquaponics system…..for just US$49.95.

Friendly Aquaponics claim that their plans and manual arose from concerns about the cost of kits offered by competitors.

Sami Grover quotes Friendly Aquaponics…….

”We were offended by the many sellers on the web who are taking advantage of people’s relative lack of knowledge about aquaponics to sell them overpriced collections of standard tanks, pumps, and piping called “aquaponics kits”, that can usually be purchased locally for a fraction of the cost. If we’d seen even ONE such “kit” that was reasonably priced, that ALSO had realistic claims about how much can be grown with it (the other problem we have with these people), we wouldn’t have bothered with this set of plans.”

The articles continues with the claim that kits costing $3,000 can be built as DIY projects for as little as US$500……using Friendly’s micro-aquaponics plans.

The TreeHugger article came along at an interesting time because I’ve had similar questions about aquaponics kits.

Some of the issues that attach to aquaponics kits include:

• The claims about their capabilities.
• The “technical” advice provided with the kits.
• The quality of the components.
• The cost of the kits.

As with anything, claims as to the performance of aquaponics systems should be treated with a big dose of caveat emptor.

Take my home state, for example.  Currently, Queensland is hot, very humid and a favourite holiday destination for many sap-sucking and leaf-eating creatures…..so growing any plant is a challenge at the moment.  In three months’ time, we’ll be in full flight and able to grow almost anything just as the rest of the country descends into winter.

There are so many factors that influence the growth of fish and plants that generalised claims – about the amount of fish and plants that can be produced – are worthless.

If predicting the amount of produce that a particular system can produce is an issue then, given the unpredictability of the marketplace, attempting to estimate the financial value of such produce is even sillier.

Talk about the return on investment (ROI) in such situations should be afforded the same credibility as fortune cookies.

The adequacy of technical advice is another issue.  The “just add water and shake” approach of some kit distributors will produce a similar outcome to giving car keys to a toddler……they may make it go but they’ll quite likely kill things in the process.

The quality of components can be an issue, too.

The first test of a tank or grow bed is that it should hold water and (as strange as it seems), I’ve encountered fibreglass tanks and grow beds that failed this basic test.

One such tank that I saw had fourteen holes in it.  Now, one hole is sloppy craftsmanship but fourteen holes is a sieve.

I’m not concerned about the cost of kits per se.  In my view, people who produce a good product are entitled to a reasonable return on their investment of resources…..and there will always be those (asset-rich but time-poor) people who are willing to pay for the convenience that kits offer.

To summarise……I don’t have an issue with kit distributors who provide quality products with sound operating instructions and a realistic assessment of the kit’s capabilities.

Where these things don’t happen, then the answer to Sami’s question is probably in the affirmative.

In any case, the absence of wealth shouldn’t be a barrier to producing clean fresh food for one’s family…..so DIY options like those offered by Friendly Aquaponics are important.

-o0o-

Interest in aquaponics grows daily.

Thousands of people throughout the world debate the various aspects of this wonderful phenomenon on a growing number of discussion forums and there’s hardly a day goes by when a new book, kit or other product doesn’t hit the market.

But there’s an elephant in the room that no-one’s talking about.

It’s SAFETY!

In terms of people safety, there are two main risks that attend aquaponics systems…….drowning and electrocution.

Several years ago, I pioneered the use of access barriers in aquaponics systems.

One of the reasons I favour square or rectangular tanks is the ease with which they can be covered to prevent entry by curious toddlers.

Access barriers keep toddlers and pets safe.

While access barriers are more widely used than they used to be, there are still far too many systems that are not adequately secured against entry by small people.

If a tank can’t be covered, it must be placed behind a child-proof fence or locked inside a shed.

Nothing will diminish the positive atmosphere that surrounds aquaponics like media headlines about a drowned child.

While small children are those most at risk of drowning in an aquaponics system, electrocution is rather less selective – it will kill anyone.

Electricity - an excellent servant but a cruel master.

I have seen hundreds of aquaponics systems and many of them have one thing in common……… a foolish disregard for electrical safety.

I’ve seen extension cords running across thoroughfares where they risk damage from being walked or driven on.  I’ve also seen plugs suspended over fish tanks, or lying near puddles, and  I’m aware of people who have built equipment or performed work that should have been done by a licensed electrician.

Don’t get me wrong.  This is not about you…..it’s about us.   This post was largely prompted by a self-audit of my own systems that suggested that I needed to lift my own electrical safety game.

A Clipsal Portable RCD Power Outlet is on my shopping list and a commitment to being smarter around electricity was prominent on my New Years’ resolutions list.

Let’s all commit to a better, safer way of doing things in 2010.

-o0o-