Backyard Aquaponics
A place to discuss aquaponics

Rupert - Janet is quite correct in that biofiltration is not going to remove nitrate. I think what you are thinking about is the swirl seperators that are incorporated into the commercial systems. Once the solids are accumulated in these filters they are then removed from the system altogether - along with any beneficial elements. It is thought that the non-removal of these solids is a reason why Joel and others have not had issues with potassium deficiency in their backyard systems (unlike their commercial counterparts).

Of course Gary's system does not have such filtration as such. Your mistake here has however made me think that part of the reason for not having nitrate issues could be solids removed out of the system altogether to the run to waste componets of the system. To answer this I would need to know whether Gary finds that he is pulling accumulated solids out of his tank when pumping removing water to his pots (I understand from what you have said Gary that you are pumping to a hose??).

Gary - as I said, I would be very interested in ore info that anybody can provide on the nitrate flashing theory. Is this something that Steve suggested - maybe Steve can give some more info. Gary can you remind me what plants you have in your F&D bed and also what your current kilo per 100 litre rate is approx.

VB

gotta go today, here's some quickies:

yes, my assumptions were all over the place, but the maths is right (fix the assumptions and the numbers will be right). I was looking at the starting value of the system as a worst case, when I start harvesting I'll be at around 1kg/100l



that's an average from a greenhouse book, shorter life means less plants. What times have people been getting here?



I assumed this. I assumed steady state - every day there is the same amount of growth and death.



half as many lettuces?



Oh, I haven't read that paper yet. should pester him for it.

The underlying premise is that given a high enough nitrate level that plant will need water and nitrate at fixed ratios (the basis of hydroponics) so there is no advantage in circulating. It would imply high stocking ratios, but to be honest I've been getting adequate results with my very low rates.

This logic seems reasonable having read about root uptake mechanisms - it is akin to putting fish in optimal brine for their osmoregulation - the plant switches to a lower energy growth form.



I forget, what are the advantages of cocopeat over soil?

Gary, I believe this statement is incorrect

Where have you explained this? How does this work?


It has to do with the level of control over the parameters... A large system that has well controlled parameters will have exactly the same level of production per litre as a small one... It's just that YOU can control YOUR parameters easier in a small system. Someone with a large system with large pumps, large blowers, large heaters, large growing area etc, can also replicate the exact same growing conditions as any smaller system, and as such produce the exact same amount of fish per litre....

It is a case of simple logic isn't it.....?

Rupert, EcoCity, Savidov and Travis do not use run to waste systems, Travis doesn't use any solids removal either so far as I know, but I'm not sure about Barramundi Blue..

EB,

You said that you believed the following statement to be incorrect:



In my post of Monday 12th, I believe I qualified that position with the following statement:

"If things (fish and plants) grow faster in the optimum conditions (and they do).....and I replicate those conditions (and I can)....then it necessarily follows that I can produce more fish per litre of water than someone who is not able to control the growing parameters to the same extent."

In prior posts, I've referred to the capacity to cover the tank, to insulating the tank, doing frequent water tests, adopting a structured feeding regime.......closer management.

As you've stated......"It's just that YOU can control YOUR parameters easier in a small system." And that's the very point that I sought to make.

Gary

Hi VB,
You asked:



I am currently growing silver beet in my flood and drain gravel bed. In my satellite pots I am growing tomatoes, cucumbers, capsicums and basil.
In my trays, I have lettuce, silver beet, bok choi, dwarf beans, thyme, parsley, onions, carrots and beetroot.

I have been harvesting bok choi, silver beet, lettuce and herbs since Friday 2nd February. Most of the lettuce bolted to seed.

On January 26th, I reported that I weighed six fish for an average of 220 grams each. This translated into a total of 9.68kg in 600 litres or 1kg of fish to each 62 litres.

In a later post, I quoted a DPI article where the figure of 40 - 50kg per cubic metre (1kg per 20 litres) was cited. I don't know if this was an aquaponic system. I'm inclined to think that it might have been a recirculating aquaculture system.

I estimate that my fish would be around 260 grams average......a total of about 11.5kg.

My 44 fish would need to grow to 680 grams for me to achieve the rate of 1kg of fish per 20 litres of water.

I can't find the source of my "nitrate flashing off as a harmless gas" information - I'll keep looking.

Gary

Gary - it has been said that using optimum fish tank to grow-bed ratios - one could stock 6kg to 100 litres in AP. This of course is a little greater than 1kg to 100 litres. In terms of recirculating aquaculture I cannot, without researching it a bit, tell you the stocking rate - but I will say that when speaking to an ex recirculating aquaculture farmer a couple of weeks ago about AP and the 6kg per 100 litres - his reaction alone clearly showed that this is substantially less than what is stocked in recirculating aquaculture. One must bear in mind though that he ran drum filters, degassing unit and ozone filtration. AP - particularly BY AP by it's nature has none of this complicated stuff - which is why it is accessible to us. I personally will be quite happy if I can grow 200 fish per year (which I will). This is 200 more thatn I ever thought I would be able to grow in my backyard before I came across AP.

VB,



I spoke about 1kg in 20 litres of water.......5kg per 100 litres.

I read this morning about 1kg of fish in seven litres of water as a maximum for recirculating aquaculture systems. This translates into 14.2kg per 100 litres.

I imagine that would require the 'full monty' when it came to equipment......and management.

Gary

I think it all comes down to money, resources, expertise and especially time to acheive the really impressive stocking densities. For most of us here with limited resources it would be harder and harder to manage and mantain parametres as the size of the sytem increases. It is also true that without constant attention and time being spent managing large systems, what we call a safe stocking density is reduced.

All it takes is a pump to fail, a heater to burn out or a pipe to come loose and potentially an entire stock of fish can be lost, unless it is constantly monitored. Cost and time spent on a system rises somewhat exponentially as the system increases. If we had the time and the money I bet 6, 10 even 14kg per 100L is possible or more!!

I think that cost is being brought down every day with the new suggestions and breakthrough ideas that are being shared here. So someday the average backyard system may be quite capable of these sorts of numbers.

My mistake - that's what I meant

Hi VB,

If I recall, it was AA who said that 6kg of fish per water was the upper limit for AP. He then went on to say that a lesser amount (2 - 3kg I think) was the likely outcome for most aquaponicists.

I read an article by Wilson Lennard where he spoke about 10kg per 100 litres (or 100kg per 1000 litres) and, more recently, I read about 14.2kg per 100 litres (for recirculating aquaculture).

I really don't know what the fish stocking limits are.......but we're nowhere near it yet. I'll probably draw the line well before my fish don't have enough space to swim freely.

At this point, I'd be happy with 5kg per 100 litres......very happy.

Gary

I think EB says in his book 6kg per 100 litres at 2:1 grow-bed to tank ratio. I can't check cause a friend is reading my copy right now.

Lennard runs his sytem with swirlers as well as screen filters (cleaned several times a day) so I don't think his extimations are relevant here unless you intend to remove solids. Removal of solids would clearly help in keeping higher levels of stock - but I personally prefer to keep the simplicity and stock at lower levels.

On the big - small discussion I am tending to go bigger and use this size to stock the same amount of fish as I could potentially have in a smaller system - but at lower density. This should help me keep a stable yet low risk system.

Ah thank you VB, it was Lennard I was thinking of not Travis...

That was (in my own muddled way) what I was trying to get across...

yes with removal of solids ala commercial setups or removal through siphon/water changes then isn't it possible that nitrite/nitrate could be lower and stocking levels higher.....

still curious though, I remember Muzza saying that he hasn't had to clean his filters but does anyone else...??

Understand the confusion I created regarding bio-filters, but I was wondering if eventually/periodically those using them found that they clogged with solids and needed to be cleaned/cleared???

I had assumed that this would be the case... not so???

Rupert - many of us use our gravel grow-beds as the bioflilters nd have not yet had any clogging issues. Joel's system has been running for years and I don't think the gravel beds have been cleaned as such (he might have raked some roots out at replanting).

Solids in a biofilter - unless removed - will break down and the nutes will end up in the system. This is why we have corrected you and said that the biofilter does not remove nitrates. Even if you ran a seperate biofilter that needed to cleaned now and again - very little nitrate would be removed in this process simply due to the infrequency of removal.

Worms in the biofilter - I have many in my gravel bed - will further help in breaking down solids and stop any likelyhood of clogging issues. I am not certain my bed will not ever have to be cleaned - the water is aweful dirty if you dig a hole in the grow-bed medium when it is flooded - but this never makes its way back to the tank (not so far). The solids in the bed are very very fine - as they have broken down fully. Any future clean that may have to be done would just be a flush out - but I hope even this will never be necessary.

Thanks VB, clears that up... I got stuck on the concept that bio-filters would trap solids and need cleaning out... the only reading/references I've seen are the commercial type systems which are cleaned constantly....

That's why I couldn't understand the advantage in running seperate bio-filters other than I assumed a reason to remove solids/lower nitrate levels... the only other reason I could see to remove solids (from what I read) is to prevent/lessen possible clogging in adapted hydro systems/trays....

So am I right in assuming that running a seperate bio-filter before distributing the water flow to hydro trays will remove some portion of solids???...

Or am I better off using a small (or series of small) mini-growbeds before the trays....

Know I could use full growbeds but my intended design will use nft channels along a wall, so thinking of maybe using a "dutch" pot or small pot before each channel

I really feel it will never be neccessary VB, the correct depth ensures the ecosystem takes care of it I am sure.