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Original thoughts on hybrid design (recovered blog)

In this blog I will try to tie together many of the thoughts that have been flying around on my blogs and discussions that followed.  I will start by revisiting some important issues that influence my thoughts around aquaponic design, followed by the presentation of arguments in favour of experimenting with component ratios.  There has been much talk around these matters.  My frustrated thought at one point was something down the line of “I understand that there is a need to have some basic guidelines for people when they start up in aquaponics, but then give them some safe beginning set-up PLUS all the reasons for having the ratios to begin with.”  Then the post of Dr Lennard’s calculator came along, and the comments that I saw about it made a very big light go on in my head.  I think there are at least two ways people set about trying to rationalize ratios, and if you are from a different mindset, the other ways of doing things appear to be, well, WRONG.  If you come from an aquaculture background and spent some time looking at the evolution of AP systems, in particular UVI, you may consider an aquaponic system to be an aquaculture filtration set-up allowing macrophytes in where you may have had to start employing denitrification stages.  If you got your grounding in horticulture / hydroponics and you look at some home kits on the market now, they look very much like a hydroponic set-up with fish tossed into the nutrient reservoir.  My belief is that it is possible then to say that people in aquaponics either think like a aquaculturalist or a hydroponist. 


I am an aquaculturalist.  When I see fish and a filter, I think oxygen supply, water flow rates, filter type, media type and surface area required.  I think feeding rates and fish food composition.  That is why I have an immediate affinity to how UVI and Dr Lennard’s component ratio calculations are explained.  Not because I think that these are the only ones that can work, but because I think like these guys do.  If you allow yourself to think like an aquaculture person first, and only let the horticulture thoughts peek through once the water hits the plants, you will look at the water movement through filter stages (media or otherwise) and aeration processes in your set-up from the following perspective:


1)      How much nutrients have been added into the system.

2)      How much metobolites will this result in the water column, and how much sludge can you expect

3)      What is the oxygen demand of your fish, and what will the oxygen demand be of the biological agents responsible for nitrification.

4)      What type of media am I using.


If you do not address these questions logically, your system design will stumble at the fish tank stage, regardless of how happy the plants may appear.  Can you see how these issues above also form the basis of the spreadsheet from Dr Lennard?  Your thought process starts at the type of food you opt for, especially in terms of the protein content.  Your feed input should be scaled to fish demand – again from aquaculture ratios – and the feed application should be done is such a way as to prevent wastage.  Ideally you want to deal with metabolites and excrement only, not uneaten food.  You could argue at this point that this line of thought is the same as going for a fish to grow bed ratio.  This would have worked for my desire for detail if it was not for the fact that through variable water flow rates and different types of media, you could support vastly different numbers of fish with the same tank and grow bed.  This may or may not be an “advanced” issue, but in terms of system components, I believe that people should know where they can stretch their system to one day.  Nothing is as irritating to me as realizing that what I have got cannot be expanded on modularly, but have to be replaced.



Having only one set of ratios to go by in the end is an incorrect assumption.  That, plus you never knew why you stuck to those ratios to begin with.  In my mind, there are no one set of ratios, but rather some important operational targets.  These are:

  1. Required water quality parameters and
  2. plant nutrient needs.


THAT IS ALL.  Component ratios are based on equipment used, surface area of media, fish stocking rates, food type, and water flow rates to mention but a few.  The correct ratio flows around in a three dimensional space and is influenced by your decisions at critical design stages.  It is far better to understand these choices than to memorise something somebody said somewhere.  Now, in order for people starting out in aquaponics, some people have become fixated on finding rules and ratios without having the foggiest notion of why these ratios are applied.  That helps nobody.  That is like the church preaching in Latin to a bunch of illiterate peasants.  To go back to an engineering comparison: You have a 1 ton vehicle that you must propel forward at 120 km/h.  You have so many choices here that which engine you pick in the end does not matter.  1000 cc, V8, Rotary, Diesel, in the end, the question was not about efficiency or cost, but simply to reach 120.  People will get all emotional about their choice of engine, but if they do not acknowledge that their opinion is based on personal preference and that there are multiple possible options, that person is being closed minded.  Now that we have the basics out of the way, we can look at ease of operation and efficiencies, about emissions and lifespan reliability, but still, there are more than one way………………….


The following points will lead us there:

  • WHY do we design aquaponic systems.  In particular, how do we knit all the requirements of fish and plants together in a single operating system.\
  • If we go back to founding statements of the technology, it is often described as the marriage of aquaculture practice with hydroponics.  To this end I want to ask: Why have we shifted significantly away from RAS filtration component ratios during this evolution of the aquaponics method.  I will visit some aquaculture designs, look at their stocking densities and media bed to tank ratios to illustrate this question.  To a large degree, this question and the first point (WHY) are intermeshed. 
  • I want to know if most people discount the network of plant roots in an NFT system completely when they calculate the surface area of their aquaponic biofilter.  We know from Lemna water treatment research that these little plants (duckweed) become a nitrifying bacteria substrate as the colony matures.  The same should apply to the roots of our raft and NFT plants.  I am now heading back to my previous posts linking my understanding of aquatic system productivity with this question.  In a way, I am starting to think that I want to have a “dirty NFT” set-up.  This will mimic what is known locally as the River-Estuary-Interface of REI.  This is the nutrient powerhouse of our systems, where nutrient laden water from rivers flow into densely vegetated sections at the head of estuaries.  The fines pack onto the exposed roots of aquatic plants, where bacteria mineralizes and nitrify the stuff and sends it downstream.  Take a look at the picture of strawberry roots inside an experimental “dirty NFT” line of my greenhouse.  Now why can we not assume that the entire surface area under water inside the 110 mm pipe will not become a huge “media mat” that can potentially have a far greater surface area than a media bed of the same proportions.

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Comment by Kobus Jooste on February 3, 2011 at 8:57pm
I was finishing off telling you about a discussion I had about monitoring gear - aquaculture vs aquarium.  One of the other members of the forum suggested a manufacturer that I looked at, but which charges 3x what a new aquarium gear manufacturer charges.  Then the debate started to go in the direction of suitability, and the view was expressed that model x was made for aquaculture and the other stuff for lightly stocked fish tanks.  The thing is that even at max stocking, AP does not nearly approach aquaculture stocking rates, thus why stick to thinking that you need to ignore the fact that there are wonderful new gear on the market designed for large aquaria.  Mercedes was instrumental with the development of passenger cars, but surely, they are not the only trusted model today. AP is a new field, where I think we will try a whole lot of things before settling down!
Comment by Nate Storey on February 3, 2011 at 7:43pm

hmm. not sure.  I'd kind of like to see the end of your response though. . .   : )

I'd finish mine, but I've forgotten what I've said.  It's usually not too terribly interesting.

Comment by Kobus Jooste on February 2, 2011 at 9:15pm
Why are our comments getting chopped?
Comment by Kobus Jooste on February 2, 2011 at 9:13pm

Thanks for that comprehensive reply Nate.  I think I share almost all of your concerns, and perhaps the ones I do not understand yet is because there are really no other people down here to tell me that I should be doing it this way or that. 


I have stated maby times over that there are a great many ways to do things, and that people should rather get on designing than to think it is all done and dusted on the invention side of aquaponics.  I am using my two systems for that, and finding it very interesting.  Below is a list of the things that I think we should be trying to achieve:


1) We are not pushing aquaculture stocking densities so get over the obsession with aeration.  Trickle towers and cascades can run any system stocked to the max of Dr. Lennard's calculator.  We should be more interested in towers and raised beds / dropped tanks.


2) We should not try to escape basic biological filtration methodology such as those employed in large aquaria.  Having some form of filtration is not breaking away from aquaponics, and it is wrong to think that the filter will suddenly cost you more oxygen because the solids (such as fines) are now being confined in a single space.  Bacteria will work on them whether they are suspended or trapped in a flow-through filter.


3) Mixed design must acknowledge the effects of plant roots, as plant and plant root action is what makes wetlands so effective.  Media surface area is not the only way to mineralize in AP, but as hydroponics keeps everything "clean", I think we are fussing too much about having rafts that look like they were filled with bottled water.  Some plants like this, but that is not what a wetland looks like.


Perhaps what we are seeing in the early days of commercial AP is the signs of competition between designers and suppliers polarizing a industry that is not sure about how the tech should look.  Kind of like an exchange I had with a

Comment by Nate Storey on February 2, 2011 at 8:19pm

Great post Kobus- You're dead on.  I think you've identified the two approaches to AP.  You're also right when you identify the problem with "rules of thumb" when there are no true standards. . . This is probably why many people are frustrated with either fish kills or poor plant production initially.  They may hear that they need 2:1 growbed volume to water vol., but may not use the correct stocking density or may be using feed with wrong protein content, etc. . .


Here's my biggest pet peeve though:  Depending on what side of the vision they fall on (aquaculture or hydroponics) design variables closely follow those of the designers focus system.  This strict adherence to their design lineage becomes dogmatic and soon you have these bastardized designs with very dogmatic beliefs regarding them.  Oftentimes this means that the system is misbalanced.

This also means that because there's no great understanding of either science, practitioners will combine hydroponic production equipment with aquaculture production equipment and expect it to work.  Instead they should redesign from the ground up recognizing that they have something new and in its own way more biologically dynamic than either of the parent systems.  This is a major problem because there are really no major AP equipment designers out there, or the industry is still so small and limited in what it offers.  In my mind it's the equivalent of bolting a plane to a car because you want a car that can fly or a plane that can drive on the highway.  It may be functional, but if you began from the ground up with solid design variables and a good understanding of what you want and how it can be accomplished, it would be much better.


The BSA of plant roots is also overlooked as you point out.  The BSA of plant roots is astronomical, and even in systems with high media BSA, dense plant roots are increasing the BSA by many times over.  We can't currently design a media that com

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