Backyard Aquaponics
A place to discuss aquaponics

Wilson Lennard wrote to me this morning letting me know that he's created a very cool modeling tool, along with an in depth "how to" document that explains how it works.

I'd like to put out a HUGE thanks to Wilson for taking the time and effort to create this super helpful tool to aid the backyard home aquaponics person. He has also made 2 different versions, one for metric users, and one for those that prefer imperial measurements.



You can download both the modeling spread sheet, as well as the "how to" explanatory notes, right now.

The metric calculator (excel) :
http://www.backyardaquaponics.com/Travi ... metric.xls

The imperial Calculator (U.S.) (excel) :
http://www.backyardaquaponics.com/Travi ... perial.xls

The How to notes (pdf):
http://www.backyardaquaponics.com/Travi ... nation.pdf

You can visit Wilson Lennards website here http://www.aquaponic.com.au

So what are you waiting for, download the modeling calculator and see how your systems stacks up to the scientific recommendations. Wilson has already run all of our BYAP systems through his modeling calculator, and our systems and stocking recommendations come in right on target. It's nice to have the independent scientific data to back up what we had always known.

See how your system stacks up and post your results here.

Great stuff Thanks Wilson

Yep, I've had a look over the modeling.... and the parameters are pretty much what has been consistantly said for years...

It will be interesting to see how the detractors and myth makers react....

And a few "overseas" systems... that from what I see, but already "knew"... fail miserably in their claims....

By the looks of it , I will have to remove solids when the fish get bigger as I dont have the surface area of growbed for mineralisation. Thats ok, with a round tank with conical floor to central takeoff , I can drain off solids like I do in the small system with same setup. The bucket I drain off the trout system daily is usually black with fish poop. The asparagus patch has loved it.

Uh....Time for a reality check. The model is very useful but doesn't appear to take into account the pH, temperature or light levels. This simplifies the model and makes it easier for us but leaves some room for future changes to the formula which could be useful as well. Getting it to where it is certainly is great and will be excellent to have - thank you Wilson Lennard

The model is designed to provide the minimum parameters to size a system for;

Removal of TAN through nitrification
Minimum tank size
Minimum flow rate
Minimum plant growing surface area
Minimum mineralisation/nutrient provision for plants

... for a given stocking and feed rate...

While pH, temperature and light effect the selection of plant types, and perhaps optimal growth...

They don't determine the factors of the model...

pH & water temperature have a correlation to ammonia toxicity.... but the model assumes complete nitrification of TAN... so as such they're also not applicable for the models purposes....

When I applied the Imperial version of the tool (hum, they don't specify which type of gallons are in use though so that could throw things off) and read the instructions pdf, it is basically telling me that I've got only 1/6th of the gravel square footage that I need and that for this to work I need to be cleaning the solids out of my gravel every 3 or so months?

So, if this tool were absolutely right, my system shouldn't be working much at all.

The flow rates recommended by the tool also seem very low. I always figured that moving at least the volume of the fish tank was important but I'm seeing recommendations for flow rate way lower than the volume of the fish tank per hour.

I think this tool could be a great think for helping get started but I don't think it is in the finished state yet.

There are explanations about how deeper gravel would be good for bio-filter and/or solids mineralization but then it goes on to explain that only the top few inches of the gravel bed actually work for mineralization so the 30 cm deep bed at the square footage given is the minimum required and even if the bed is deeper, it still must have the same square footage? This is a big sticking point with me here. I've got deep beds mostly now and I've not seen an increase in problems since I switched to the deep beds. If my system were having issues with anaerobic areas (and since I don't wash my gravel out 4 times a year, according to them I'm in trouble,) I should be seeing elevated nitrite in the big system (due to the anaerobic areas converting nitrate back to nitrite to be offgassed,) this has not happened.

There are too many other variables to boil it down this far, their methods are heavily skewed to raft and solids removal for their production and it definitely shows when you try to boil that down to recommendations on a media based backyard system. How many backyard growers net out and weight their fish weekly to figure out what amount of food to properly give them?

except for removal of TAN through nitrification which as you noted

The model does assume that these will not be the rate limiting factor and that is why they are not included. The model also assumes that dissolved oxygen will not be a factor or the actual type of bacteria that are in the bed because we aren't even really certain they are the same everywhere these systems are located. I also wondered about the bed depth as TC did and the change in water level of the bed - what affect do these have? Hopefully most of these will be factored into this model at some future point because any of them could be rate limiting under certain conditions. The model is still very useful. In the meanwhile it's important to see these limitations and know that they exist.

So does anyone know the specific surface area of Hydroton?

Hmmm seems I just need to read more... Lecca is hydroton. 250 is the answer.

I'm quite confident that, although not explicitly stated, Dr Lennard has determined the underlying oxygen demand for both general fish metabolism, feed conversion and waste nitrification in determining his formulas....

DO is implied within the feed rate, protein percentage and filtration variables for the given stocking density...

In general, correctly sized flood & drain systems have been found to provide adequate oxygenation by design, but we always recommend installing supplementary aeration.


Yes we are.... the "nitrogen cycle" and associate bacteria... are universal.... although recent research shows the bacteria concerned are not those that have been assumed and accepted for decades...


These factors are reported in his notes relating to "flood & drain" systems drawing oxygen down deeper than the first few inches..

And the "flood & drain" model just simulates a natural "rain & dry" cycle.... which inherently alllows oxygenation by the lateral roots of the plants... which are their means of oxygen adsorbtion... and as noted... occur within the top few inches of the media, even in soil...

Regarding oxygenation... from the authors notes...

Almost:
Hydroton, Canna Clay and other Brand or Trade names, are all L.E.C.A.
which is an aconymn for: Light Expanded Clay Aggregate.
Cheers IanK

I think you've missed my point. Everything I mentioned is a variable but not all are treated as variables IN THE MODEL. I understand that he knows this and I accept that this is reasonable because the model would quickly become to complex otherwise. I agree with your statement;



as far as it goes but the temperature is assumed. So what happens if we follow the model but our temperature is higher? We may end up with dead trout because the DO was inadequate for them at the higher temperature. We really haven't dealt with all the complexity of the actual system with regards to DO because of the temperature assumption.

I can't say that I'm up on the literature regarding nitrogen cycle bacteria but I'm not willing to concede the point. I will say that I don't think it matters that much with regards to our discussion. Bacteria have variation within a species and breed much faster than humans. When you add selective pressures such as temperature, ph etc to the bacterial mix in a relatively closed system like aquaponics I believe you will quickly select for those individuals that are best suited to that particular environment and that they will be the majority. Different system, different selective pressures and possibly drastic differences in bacterial processing ability. This might explain why some systems handle cold temperatures or high pH better than others.

On the last part we need some type of quantified processing ability per inch of wetted media so that the model works better for those who have deeper grow beds. It would also help to know if processing is uniform throughout the bed or stratified.
If this can be quantified people with limited space could design their systems with deeper beds to compensate and improve their system capacity without flying blind.

Yeah it would be nice but you are talking about at least two phds of research there.


From the begining of my ap days I,ve toyed with various ideas for deep gravel beds principally so that all that big nasty heavy stuff could be kept in the one spot out of the way of my plant production.