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PostPosted: Sep 29th, '08, 06:24 
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Seriously, this cant be healthy.
Seriously, this cant be healthy.
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No probs Frank :wink:

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PostPosted: Sep 29th, '08, 08:47 
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I think it's all very well to discuss the theoretical side of this, but without actually trialing different methods everyone is just guessing. There are so many factors to take into account such as root matter, solid waste accumulation, worm activity, etc, that really, it is just guessing. And trials on media beds cannot be done in only 12 months, this is where I feel Dr Lennards research has some flaws. He compared flood and drain to continuous flow beds and concluded from his results that continuous flow beds perform better. I've found that over time continuous flow beds are far more prone to clogging with solids.

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PostPosted: Sep 29th, '08, 09:07 
Just because I'm arguing the point.. or disagreeing with you doesn't imply any "emnity" Frank....

I've even agreed with you on points... :lol: ... and tried to throw in the odd smilie to ensure context :wink: :lol:

So... I'm confused Frank... It appeared to me that you were in fact arguing that the 30cm depth for growbeds was both inefficient and un-needed...

Rather, that in fact, bio-filtration was better served by a large physical surface area, which could be no more than 1cm or a thin layer... even suggesting that NFT... a thin film was sufficient to provide bio-filtration..

hygicell wrote:
Quote:
300mm seems to be a good MINIMUM depth.

NFT systems seem to contradict that
nitrification is all about surface and aeration, not about depth


Agreed, a thin film in NFT (anything from 5cm - 50cm) may provide some bio-filtration...

And across a table (usually - 12mtr x 2mtr) provides a large surface area... however I believe that the same volume of bio-filtration "potential" can be acheived just as successfully by concentrating the filtration into a greater depth.. a smaller physical footprint... a growbed....

I'll admit to having not had the time to read all the links in your spreadsheet... in fact I wasn't even aware that you had included them..... P.S. using a hyperlink to the references would make life easier... :wink:

But I suspect, and I'm happy for you to correct me.... one of the references contains data that shows that nitrification takes place in a "thin layer of water"....

And I have no problem with that what so ever Frank... it's been discussed in several post in the past and accepted as such.....

But if it's the article I believe you're referencing.. it's postulated in the context that this occurs in a thin layer "surrounding" the media... not actually on the surface (area) of the media, as is often incorrectly implied....

Hence it could be extrapolated that no media at all need be employed and that the physical surface area of the "container" was sufficient to provide the means of bio-filtration via a thin layer of water attached/contained...

I merely argue that the larger the surface area of "media" provided, the greater the bio-filtration potential....

And that this can be acheived by concentrating the media (of greatest surface area) into containers of depth rather than a large "thin" surface area.... providing maximum filtration potential... in minimal physical surface area....

The potentially best media in terms of surface area of media to actual physical area is undoubtably sand.... which has, even if the mechanics were not completely understood, been utilised for this purpose for ages...

But for reasons of channeling and the developement of anaerobic conditions... and for ease of use within "smaller" footprints... other media have been developed or utilised...

As is the case and employed by flood and drain growbeds...

The original 300cm depth arose from the early work in the "Bengal" system of growing tomatoes hydroponically in "flood and drain" gravel "growbeds" ... as postulated by James Sholto Douglas...

I question the assertion that oxygen is depleted once the nutrient water has passed through a layer of "healing" media and that depth is therefore irrelevant and ineffective past a certain point....

Or at least question the postulation that this is so within the 300mm that is commonly employed and recommended...

Perhaps there is a theoretical limit... and this is undoubtedbly true in terms of developement of anaerobic conditions...

The use of "fluidised" filtration systems that suspend the media.. is the hub of bio-filtration methods almost universally employed by external filtration systems... whether that be in aquaculture, aquaria, koi ponds or even in aquaponics...

And its done so to prevent problems of channeling and developement of anaerobic conditions...

But the use of flood and drain techniques in aquaponic growbeds... acheives exactly the same result... and can be done so, utilising "depth" rather than expanded surface area...

Ther are many examples of member systems that employ depths greater, or even shallower than 300mm ... and they do so quite successfully...

If the arguement is that it is just as efficient in terms of filtration to utilise vast areas of thin media... then fine... I have no doubt that it will work...

But, I think it also raises other questions and concerns as to efficient filtration potential when employed practically in limited spaces available to backyard systems...

And I've seen no evidence to suggest that the accepted methods of flood and drain... usually with a degree of depth.. are either ineffective or detremental.... in terms of either filtration, oxygenation, solids breakdown, plant growth and/or yield...


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PostPosted: Sep 29th, '08, 13:12 
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I think we are basically agreeing with each other, Rupert
just talking over each others head
so let's stop this discussion as I'm sure we both are weary of it and so are lots of other readers

frank


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PostPosted: Feb 11th, '09, 05:11 
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Not wishing to revive the surface area/depth debate, but.......

The thing that is being neglected is the speed of water flow over the media. This is why I suspect (observation based) that media based continuous flow systems (which tend to be slow flowing) are more prone to clogging than flood and drain, and why fast draining F&D systems clog less and oxygenate better than slow ones. Not only does the faster moving water move gunk through the system, but it would oxygenate better and have less chance of providing anaerobic spots.

So in putting this theory to the test I will be trying some deep (900mm) GBs with coarser basalt gravel (+/-25mm) for the bottom 300mm, 12mm bassalt for the middle and hydronton for the last 300mm. BTW best price I have received for the hyronton is $28 a bag in pallet lots.


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PostPosted: Feb 11th, '09, 09:09 
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mcfarm wrote:
BTW best price I have received for the hyronton is $28 a bag in pallet lots.

how big is a bag?

frank

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PostPosted: Feb 11th, '09, 10:13 
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50L


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PostPosted: Feb 11th, '09, 10:29 
That's a pretty good price... even for pallet lots @ wholesale.....


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PostPosted: Feb 11th, '09, 17:25 
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mcfarm,
Was the hyronton sourced locally or over the phone with delivery charges on top of that?

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PostPosted: Feb 11th, '09, 17:51 
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Locally sourced, ex Canberra - South Pacific Hydroponics. No freight, I'll pick up from them with me truck.


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PostPosted: Feb 11th, '09, 17:54 
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Seriously, this cant be healthy.
Seriously, this cant be healthy.
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Jees there must be a lot of pollies growing cash crops in canberra :P

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PostPosted: Feb 11th, '09, 19:39 
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mcfarm
Do you know where its made? Just trying to see if i can get it for the same price where im from

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PostPosted: Feb 11th, '09, 21:42 
Expanded Clay is made in Belgium... or Germany.... or Holland.... depending on brand...

There is a cheap "Chinese" brand... but most suppliers don't bother to carry the stuff anymore...


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PostPosted: Feb 11th, '09, 22:04 
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There is also a commercial version used in the concrete industry. Its not round and pretty, but its light and cheap. Lightweight concrete aggregate is also expanded clay and often made more locally. A friend of mine is using it in his hydroponic beds. I have not tested it to see how inert it is, but hey it works.

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PostPosted: Feb 12th, '09, 03:49 
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Adrian wrote:
mcfarm
Do you know where its made? Just trying to see if i can get it for the same price where im from


Sorry no. Will check when next in Canberra (I live in NSW on a farm). All I remember is the bags were labelled Hydroton on light blue writing on a white background in predominantly clear bags. Not happy if it's from China, they don't have a good track record on keeping things clean. Mind use cooked clay can't be that toxic???


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