Aquaponics’ Biggest Mistake

Most people who are interested in aquaponics know that Missouri farmers Tom and Paula Speraneo popularized what is commonly termed flood and drain aquaponics.

For the uninitiated, flood and drain aquaponics in its simplest guise comprises a fish tank and one or more media (usually gravel) grow beds.  Nutrient-rich water is pumped from the fish tank into the gravel grow beds before draining back into the fish tank.  This is the most widely used aquaponics configuration in the world.

What far fewer people know is how the Speraneos came to be involved in aquaponics and where the idea for their basic flood and drain system originated.

Following the completion of his PhD dissertation at North Carolina State University, Mark R. McMurtry undertook a series of trips to showcase iAVs and its benefits for allied faculty staff, students and aquaculture industry professionals.

In December 1989, one such trip to Arkansas put Mark in contact with Tom and Paula Speraneo at the University of Arkansas in Little Rock.

A week later, Mark facilitated a 3-day interactive discussion/workshop at the Meadowcreek Project in Fox, Arkansas for the usual mix of faculty, staff, students and other interested parties – including the Speraneos.

The Speraneos returned home keen to construct an integrated aquaculture system based on what they’d learned from Mark.

As it turned out, they weren’t able to afford the sand that was central to iavs’ effectiveness, so they dug up their gravel driveway for use in their system bio-filter.

Let’s remember that the efficacy of iAVs relies on the use of sand (not gravel) so this was a significant change and one that would have serious implications for aquaponics.

Meanwhile, oblivious to the fact that his work was about to be usurped by a mistake, Mark had begun a promotional tour of sub-Saharan Africa and Middle Eastern countries.

When he returned, he became aware of the Spereaneo’s substitution of gravel for the sand and he counselled them at length about their choice – but they persisted.  This aberration would subsequently be popularised as the flood and drain aquaponics system.

This “mistake”…..subsequently to become willful ignorance…..was what best-selling author Malcolm Gladwell would come to describe as a “tipping point” – one that would have profound, negative implications for aquaponics.

The sand bio-filter is the heart of the iAVs “living machine”.  The substitution of gravel for sand impacted the efficacy of the original iAVs in several ways including:

  • significant reduction in mechanical filtration capability
  • significant reduction in soil organism populations  and activity
  • reduced aeration of media bacteria and plant root zone
  • reduced nutrient utilization and system stability
  • significant reduction in fish survival, feed rate and growth
  • increased capital costs with reduced fish and plant yields
  • increased operating cost per unit of production

One of the key features of the iAVs design was its versatility.  The same system design could be used by a backyard farmer or an impoverished villager or a protected cropping greenhouse operator.

The first casualty of the change in media was iAVs’ commercial potential.  

The basic flood and drain system never gained commercial traction because gravel does not lend itself to the mechanisation and automation that is a feature of controlled environment agriculture.  Sand, by contrast, has been used in hydroponic greenhouse culture for decades – subject to all of the usual constraints associated with greenhouse culture.

The iAVs could be built and operated by a humble villager with some seeds and little guidance.  The basic flood and drain system, by contrast, requires a connection to the grid, a pump (or two) and ongoing access to mineral supplements.   The basic flood and drain system also requires greater skills and knowledge arising from the heightened risks that it poses.

As an aside, the Speraneos (who initially gave credit to Mark for their introduction to what was yet to become known as aquaponics), eventually used their utilisation of gravel as a point of sufficient difference (in their minds at least) to assume ownership of the concept.

This process of taking a system design and “tweaking” it (with a view to assuming ownership of the idea that underpins it), was to become a recurring theme in aquaponics.

Anyway, the Speraneos developed an information package and promoted their system through an Internet mail list (the forerunner of the discussion forum). 

In 2005, Joel Malcolm bought the Speraneo’s information kit and “tweaked” it into an Australian context.  Australia’s ABC Gardening TV program ran a segment on Malcolm’s home-based system and the basic flood and drain system enjoyed a new surge in popularity.  Regrettably, however, the “new” flood and drain system had the same basic flaw…..the media particle size.

The Speraneo model was adopted by various other kit makers and, while they “tweaked” the model too, none of them managed to grasp the toxic tipping point…..the gravel or expanded clay pebbles.

To summarize, the substitution of gravel (or clay pebbles) for sand was not just a minor detail – it was the aquaponics difference between chalk and cheese.   The iAVs is a living machine whereas the basic flood and drain system is, given a convergence of common events, a killing machine.

In terms of its filtration efficacy, Mark has characterized the use of gravel (as distinct from sand) in the biofilter as “attempting to catch BB’s with a basketball hoop.”

So, the basic flood and drain aquaponics system was/is nothing more than a major mistake.

Notwithstanding its noble bloodlines, the basic flood and drain system is actually an unfortunate mutation with nothing like the productivity, resilience and versatility of its iAVs predecessor.



  1. Wish I had been aware if this IAVS concept before setting up my gravel filled F/D system. Even with a functioning RFF my GB’s eventually become anaerobic from all the fines that are not captured by the RFF and eventually settle into a dead zone in the beds. I chuckled at your B-B/Basketball net analogy, which is quite accurate. Makes perfect sense, to me, anyway, that the sand will keep the “stuff” at the surface where nature can do it’s magic instead of allowing the beds to fill from the bottom up with plant killing trash.

    “Can’t wait” till I can get my setup redesigned for iAVs.

    • BH…Never mind, the best lessons in life invariably exact a price. Mark and I advise everyone who has an AP system (particularly those who think they’re working) to build an iAVs with which to compare. We’re confident that they’ll opt for iAVs for all future systems.

      The new system will be all the more satisfying when you get it up and going. In the meantime, take the opportunity to plough through our content….and to ask questions as they occur.

  2. Hi Gary, while I understand that sand as a media is better by virtue of its much increased surface area, it does not seem to me that hydroton or lava rock are failures as this article seems to imply. I have great success in growing many variety of plants using both in F&D systems. The growth rates are phenomenal. So although sand may give better results other methods should not be charactorized as a “killer machine.” Once my current cr is done I will transform by dutch bucket system into a sand bed system. My sole concern is the use of coral sand and the resulting Ph.

    • Jim….Let me begin by defining what I mean by “basic flood and drain.” This is any media bed system that is not fitted with dedicated mechanical and biological filtration. This is where the water travels from the fish tank to the media beds and then back into the fish tank (sometimes via a sump tank).

      In my view that system is a prospective “killing machine”…..and there are hundreds of reports of dead, dying and sick fish to support that contention. In the context of iAVs, what I call the basic flood and drain system is a mistake, an aberration or a mutation.

      The Speraneos, the people who popularised the system, were specifically counselled against it – but they persisted – and the world has had to live with the mistake ever since.

      Gravel, hydroton and lava rock are all fine if the system is fitted with dedicated filtration…..if you’re prepared to accept that it will cost you more to produce less food than you could with an iAVs.

      I confidently predict that, once you’ve tried sand bio-filters, you’ll be as enthusiastic about them as we are…..and that’s all we ask of anyone who questions our claims. Just try it.

      Jim, the sand that you use must be inert…..coral sands are not suitable. I suggest that you look at the black volcanic sand that is to be found on the beaches adjacent to the Waipio Valley. That may be better for iAVs purposes.

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