I'm going to add this as a blog and discussion in the group, but thought that I might get some more ideas if it is "out there" in the whole group.

 

It struck me the other day that we have pieced together a lot around mixed aquaponic design without dedicating any discussion to the thinking behind mixed aquaponic systems at all.  A picture of my system, ever evolving, adorns the group page but what is it all about really?

Well, to start off with, here what it is not.  It is not a Friendly/UVI style raft-based or Dr Lennard’s calculator-based media system in terms of scaling.  It is not a barrelponics unit and it is not any other possible kit that is out there.  A mixed system, my mixed system, is a unit containing elements of aquaponics in scales or ratios that is still rather ill defined to say the least.  In this discussion, I would like to list what motivates my design thoughts, and then I would like to encourage feedback from all the members.  I do not want to dictate, thus it is up to the individual member to decide what he or she thinks a mixed design system ultimately represents.  Here are some of my original motivators:

 

  • Most AP designs are expansive.  I wanted to look at working in a small footprint.
  • Gravel beds are very versatile filters, and as time has shown, simple and effective
  • NFT / raft beds have shown to be highly productive, often more so than gravel beds according to some authors.

 

Throw it all together and I wanted a small footprint system with the filtration and nitrification characteristics of a media bed unit and the growing capacity of raft/NFT.  In time, some more thoughts came about. 

 

Raised beds: Raised beds allow for space underneath to be utilized for all kinds of things.  In my unit, I work with a steel support structure and the space underneath was first just storage space or empty.  Then I got the idea to add some bio-filtration capacity by adding filters underneath some of the beds.  The raised beds also allow the cascade aeration I like to use to be more effective.

 

Sand beds: This is a new development for me.  My gravel beds are completely effective for mineralization and nitrification (more about this later) and therefore I can play with additional media options that are not crucial for filtration but act only as a growth media.

 

In the end, I realised that I was working with a “core and periphery” type design here.  Some components are crucial to my system’s functioning, while the rest are there to exploit the growing capacity of the space and the nutrients in the water.  For me the “core” is the fish tank (I have no sump) and the media beds operating continually to act as filtration, mineralization and aeration zones.  The periphery is everything else I can shove into the system’s footprint. The graphic below represents what I see as "core" and "peripheral functions of my unit.

 

 

In my unit, the media beds were scaled according to Dr. Lennard’s calculator.  This means that the system, stripped of everything else, is still likely to be stable if there was only the fish tank and three gravel beds as structures.  The core is therefore stable, but small, allowing for peripheral, high density structures to try to maximise the use of the nutrient enriched water.  The image below is a representation of what I see as "core" and "peripheral" structures in a system such as mine.

 

 

As peripheral structures, I have had a raft bed before, which has now become the sand bed, a small always flooded gravel bed for watercress, a small media-less bin for duckweed (it holds just a snack volume, not sufficient to replace feeds), NFT, the bio-filter, a stacked NFT that is about to come out to be replaced with four compact towers.  The bio-filter was born from an observation that the fine particles in the water stream makes it through the gravel.  I wanted to trap this somewhere and hence the attachment of the filter next to the fish tank. 

 

As stated before, I wanted to cram a lot of growing capacity in a small space.  My original goal was 40 tilapia and 200 plants in a footprint of 3 square meters.  I have attained this in bursts but have never been able to sustain it due to a number of different issues – lighting inside the space becoming insufficient, structures not performing optimally, etc.  The addition of the sand bed and the four compact towers, each capable (in theory) to support 12 plants, are bringing me closer to that original design goal again.  Anyone interested to add thoughts or ask questions is welcome to throw it out there.

 

Tags: aquaponics, concepts, design, mixed

Views: 270

Replies to This Discussion

That was nicely presented, sir. ;-)

Hi Kobus,

It's still mind boggling to consider your plant/space/fish ratios. I have almost the same footprint(4 sq meters) with only 10 fish and 40 plants(light herbs). The division in function with your coining of "core/periphery" seems obvious now as we move outward from the rules of thumb standard with more intensive waste/nutrient utilization in this mixed system. The trial you've done here, this far, is spectacular, if we consider this on larger scales. BTW, i like the graphics(self explanatory),should be saved in the "mixed rules of thumb" section? 

Thanks for the complements Izzy and Harold.  I have not been able to stabilize around the plants, thus cannot claim 200 constantly yet.  The 40 fish is stable though - Ammonia 0.91 mg/L, Nitrate and Nitrite 0.00 mg/L.  I have a suspicion that the passion fruit vine will also limit my ability to push the plant side.  It currently carries 100 fruit.  The max plant yield came from watercress, strawberry, lettuce and spring onion, which allows greater densities than most other plants.  Until I can get a number of cycles in a row though, I will never consider it as objective obtained - it is still illusive, but attainable I believe.

 

I think we have to wait and see who else has design ideas before we make my concepts a rule though.....

Harold Sukhbir said:

Hi Kobus,

It's still mind boggling to consider your plant/space/fish ratios. I have almost the same footprint(4 sq meters) with only 10 fish and 40 plants(light herbs). The division in function with your coining of "core/periphery" seems obvious now as we move outward from the rules of thumb standard with more intensive waste/nutrient utilization in this mixed system. The trial you've done here, this far, is spectacular, if we consider this on larger scales. BTW, i like the graphics(self explanatory),should be saved in the "mixed rules of thumb" section? 

Hi Kobus,

Really impressive system.  How large is your tank for the fish and what size fish are you able to produce?  You mentioned something about a seed germination bed, is it possible to have a fish equivalent to this?  Maybe the space under some of your raised bed could function as a hatchery for fingerlings.  Just a thought.

Thanks Chris

 

It is based on a 1000 liter IBC, but configured in such a way that the max water level is at 950 liters (one of the sumps overflows at this point).  The system is constantly evolving and now has a few components not in the picture used in the post.  I have a 180 liter mineralization sump and a 120 liter clear water sump attached to either side of the IBC to increase water volume and to test some ideas.  The mineralization sump (full of floating media) catches a lot of fine floating solids which I leave in there to mineralize, while the smaller sump acts as a source of filtered water for my NFT lines.  The bed in front (then with lettuce) is now an experimental sand bed, while the tripple 110 mm pipe stack in the background has now been replaced by a compact tower.  The gravel bed on top of the IBC tank (small red one) is an always flooded bed for watercress, while all the other remaining gravel beds are flood-and drain.

 

I run the system with 40 tilapia (mozambique) which should reach a weight of 500 grams (about a pound?) but they are not all that size - it is thus designed to handle 20 kg's of fish.  The media beds are scaled to about 100% of what is recommended in Dr Lennard's calculator, thus about 2.8m2 of gravel bed area (for fruiting crops, I'm supposed to have 2.7).  The sumps and NFT are "extra" and thus I have more than adequate plant to fish water ratios even with a relatively high fish load. In the picture of the system, in the back left bed there is a small steel trellis with a little clump of green at its base - that has now become a monster passion fruit vine that dominates the back of the system and really sucks nutrients and water out of the unit at an allarming rate, but helps a lot in maintaining water quality.

 

The sand bed can double as a germination bed if it carries on working.  The Aussies typically use a header tank in many of their designs to add pressure but also to act as a fingerling tank.  There is more than enough space under my beds to still slot in a fingerling tank as well - you are right.  I have not reached that stage of efficiency yet.  

Chris Gannon said:

Hi Kobus,

Really impressive system.  How large is your tank for the fish and what size fish are you able to produce?  You mentioned something about a seed germination bed, is it possible to have a fish equivalent to this?  Maybe the space under some of your raised bed could function as a hatchery for fingerlings.  Just a thought.

Great description Kobus!  The added insights in your reply comments add value too.  I have just joined the community and am in the planning stages of a system.  My vision before stumbling upon this group was much like the system you have built.  One thought that I had to gain maximum plant volume was to add a number of aeroponic towers to my system between where you have the filters and the inlet to your fish tank.  As the water coming out of filter (at least in concept) is particulate free it seemed to me to be the ideal place for adding aeroponics as the nozzles in those units can be easily clogged.  Aeroponic units should have a low impact on water quality.  The one thought that I had was to add aeration to the post filter tank before pumping to the aeroponic towers to get as much suspended oxygen into the solution as possible. 

Any thoughts on this idea are most welcome.

Bob - thanks for the feedback.  In a previous system I had (an expansive one) the gravel beds drained into rafts, and although some solids still made it through, the roots of the plants stayed relatively clean.  If you want to run aeroponics after a bed (I'm assuming) that there will be a secondary pump, which, if screened, should take care of the little bits that may sneak through.

 

One of the ideas I was testing with the new system here was to have raised beds and cascades into the FT, negating the need for aeration.  This has worked, but also cut the option of adding "something" to the clean water line coming out of the gravel bed.  Since deciding to expand on the amount of NFT (and add towers) in the unit to increase the planting space without crowding the few gravel beds that I have, I have beed adding some more sumps.  I am not quite done, but the idea is to have a "dirty" line and a "clean" line by the beginning of my warmer period (Spetember/October).  I have added the sand bed, and the sump for the towers and the concept aeroponic line.

 

Looking forward to finishing it, and seeing how your system develops.

 

Regards

Kobus 


Bob Segraves-Collis said:

Great description Kobus!  The added insights in your reply comments add value too.  I have just joined the community and am in the planning stages of a system.  My vision before stumbling upon this group was much like the system you have built.  One thought that I had to gain maximum plant volume was to add a number of aeroponic towers to my system between where you have the filters and the inlet to your fish tank.  As the water coming out of filter (at least in concept) is particulate free it seemed to me to be the ideal place for adding aeroponics as the nozzles in those units can be easily clogged.  Aeroponic units should have a low impact on water quality.  The one thought that I had was to add aeration to the post filter tank before pumping to the aeroponic towers to get as much suspended oxygen into the solution as possible. 

Any thoughts on this idea are most welcome.

The more I mess around with my system, the more I think that I had overdone the fish.  It took taking them all out for overwintering to get the strawberries to flower.  I am in the process of adding some towers, and will hopefully get round to the aeroponic unit before Spring.  This should add 60 - 80 pot spaces in the system.  Then I will be dropping the fish population by 25% and plant the gravel beds more sparsely.  My current ultimate goal is to match mineralization and ammonification ratios with Dr Lennard's calculator, and then max out NFT components until I see nutrient stress.

Hi Kobus,

Gravel beds are the main bio-filtration and at the same time "solids digestion" in the AP. Adding too many roots in these beds will become counter productive(oxygen, nutrient availability, space for solids accommodation )at some point. One of the methods for control I see the operator having, is dedicating specific plants to specific beds through his knowledge of particular plants, their nutrient demands and root structures. As you have commented in the past, plant densities are outside our rules of thumb calculator, and is a grey area only actual experience can address. BTW I have also reverted to ROT ratios for fish. As you said, your fish ratios will fluctuate for you because of seasonal changes in your country. Mixed AP allows us to maximize our utilization of system nutrient by having the right balance of root density in our beds so that we can use NFT, DWC, Towers etc. for growing more plants than if we were confined to beds alone..

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