The Basic Flood and Drain System (which I refer to as the Speraneo model in recognition of the man who popularised it) is the most commonly used backyard aquaponics system in the world.
It is simple to understand, easy to build and operate – and (within particular constraints) it works.
Other factors that have contributed to its success include:
- clever adaptation of the basic recirculating aquaculture system.
- the use of tilapia.
- the systematisation of the concept.
- vigorous promotion by manufacturers of aquaponics kit systems.
Tom Speraneo realised that he could take the flood and drain grow bed (long used in hydroponics circles) and adapt it to:
- capture and mineralise the fish solids.
- facilitate nitrification and aeration.
- grow plants.
Tom Speraneo’s choice of tilapia as the fish species for his model was inspired.
In fact, I’d go so far as to suggest that they were central to the success that the model has enjoyed. Not only do they have a legendary reputation for their ability to survive in water of sub-optimal quality, but they also breed easily. This is a significant benefit for those seeking “cradle to the grave” backyard food production.
Speraneo also formularised his concept to include component ratios, grow bed depth and stocking density guidelines. This made it easy to replicate the model and to scale it up or down.
Local entrepreneurs were quick to see the potential of the basic flood and drain system – and several Speraneo facsimiles emerged accompanied by vigorous promotion.
OK…..it all sounds very positive so far…..so what’s the problem?
The multi-function grow bed that is at the heart of the popularity of the model is also its principal flaw.
The simple fact is that the capture/mineralisation role of fish solids is at odds with the nitrification/aeration function. Bio-filters work most effectively when solids loadings are minimised.
To a large extent, this shortcoming is offset by the robustness of tilapia.
So, what happens if you live somewhere (like Australia or some US states) where tilapia are a banned species…..or you live in a cooler climate unsuited to tilapia?
Quite simply, if you take tilapia out of the equation, the Speraneo prescriptions around component ratios, grow bed depth and stocking density become almost worthless.
Some kit manufacturers apparently failed to grasp this issue and ploughed ahead with the promotion of the original Speraneo prescription.
I began to suggest that, in order to grow useful quantities of fish, a flood and drain aquaponics system would need mechanical and supplementary biological filtration.
Since that didn’t accord with the local kit makers’ view of the world, those suggestions were derided – and so the onset of summer and the occurrence of fishkills became increasingly synonymous with each other.
Convincing people of the need for solids removal has been a hard row to hoe.
It’s only now, after years of beating that drum, that the idea has begun to gain traction – so the growing numbers of people who have now started to fit solids removal devices to their systems is personally satisfying.
While the best way to achieve productivity and resilience out of a flood and drain system is to equip it for solids removal, there are still those who find the basic Speraneo model charming in its simplicity…..or those who couldn’t easily modify their existing systems.
So, how do we set up a basic flood and drain system so that it works – regardless of the species?
We’ll talk about that in my next post.