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Depth of grow bed????

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Hi,

I don't have a preference for grow bed depth because I like filtration in the mix which tends to make the depth of the bed a little redundant and I can pretty much do what I like. Take two examples, I have tomatoes growin both in my wheel barrow and in a gravel bed. The wheel barrow is about 250mm deep with soil and the gravel bed is 500mm deep.

Both of them require I support the plant with string or it creeps accross the ground. The actual depth of the bed makes not one iota of difference aside from evaporation and possible temperature. Though the temperature can be avoided with the right water exchange in the bed.

Below you will find a link to a short article I wrote on aquaponicsWA or hyrdoponicxpress when I visited last year. These guys have some decades of experience with hydro so the step sideways to aqua... is relatively simple and they are growing trees in 150mm hydro trays. Take Shannida and Matt Herbert from aquaponics.com.au who have been doing this in the same hydro trays since 2006....

Gotta wonder wonder what all the hype on deep beds is all about? Consider this, you can provide the same biological filtration for for 100kg of fish being fed 1kg of feed per day with 100 litres of bio media it cleans itself and does its thing without you doing anything. Just dump it in a blue drum with an air stone and away you go...

http://www.earthangroup.com.au/hydroponics-xpress-in-wa/778/

Makes you wonder why the expense of strong beds to hold twice the volume of water and expanded clay, not to mention twice the cost on the amount of clay you need. When half the depth of bed running continuous flow has no problem growing trees.... Yeah 300mm beds in the back yard, in my opinion is hype and completely unsustainable, if your preference is to provide inexpensive fresh and safe food to your family.

Regards

Paul

Edited by Earthan Group (see edit history)

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So what I'm hearing is that based on years of trial and error, the majority of people feel that a shallow grow bed with a good bio filter is more efficient?

Based on these years of trial and error, what is the most efficient bio filter?

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So what I'm hearing is that based on years of trial and error, the majority of people feel that a shallow grow bed with a good bio filter is more efficient?

Based on these years of trial and error, what is the most efficient bio filter?

Probably a Fluidized Sand Bed Filter because of the superior surface area of the media (sand grains). Next, probably a plastic media filled fluidized bed filter (kaldness, plastic beads, bio pellets, etc.).

As EG mentioned a few posts up, a 55 Gallon Drum filled with plastic media and an air stone with reasonable air flow works extremely well, and can be quite affordable (depending on your media choice). Fluidized sand bed filters are also quite easy to make, but they do require some pressure in order for the sand to actually fluidize. They require a LOT of pressure for initial fluidization, but then can run using less pressure usually to maintain the fluidized state. Sand is also much more likely to channelize than plastic media. Plastic media based filters tend to require less monitoring, but the sand filter generally outperforms them, so it's somewhat of a matter of what fits your needs and time requirements best.

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Hi Littlewolf,

So what I'm hearing is that based on years of trial and error, the majority of people feel that a shallow grow bed with a good bio filter is more efficient?

If you're talking about the majority of people right across the worldwide aquaponics community, then you're probably talking about 300mm (12") deep beds and no filtration - what I refer to as the basic flood and drain system. It's the most common for no other reason than the fact that it's been the most vigorously promoted by kit manufacturers.

APHQ is where the focus has always been on the use of filtration. Our position is supported by science and simple logic - rather than belief and tacit acceptance of what you're told.

If you set your system up as a simple recirculating aquaculture system then you are able to use any mix of growing systems that you like - and you have the added benefit of being able to isolate the fish side of your system from the plant growing part (very useful in disease or infestation control and managing heat loss).

Based on these years of trial and error, what is the most efficient bio filter?

As Kellen said, a fluidised bed sand filter is probably the most efficient but, for backyard purposes, a moving bed bio-filter offers the best mix of efficiency and simplicity (of construction and operation). I've also successfully used trickling bio-filters for years.

I notice that you haven't listed a location for yourself. If we know where you come from, we can probably factor your climate into the discussion.

Gary

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some questions for continuous flow media bed

 

 

Most of them use a submerged pipe running the length of the bed with small slits cut in the pipe, and there are drains on both ends of most of them. I originally had set them up to be bog filters filled with aquatic marginals, and then changed plans and thought I'd try them as traditional GB's and they've worked great. 

 

1. At what depth from the top of the surface would you place this pipe.  I understand it depends on the media, for discussion lets look at 3 (Sand, 3/4 gravel and clay pellets or hydrotron).  

2. Does the depth of the pipe matter if the depth of the grow bed changes?  From the above discussion a grow bed depth of 150 -300 mm is sufficient for most applications. So for this example 150 mm depth and 300 mm depth.

3.  What flow rate should be used or does it matter?

 

Thanks,

Clint

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Hi Clint,

 

All of my post 2009 media grow beds were sub-surface continuous flow so I feel qualified to respond to your question.

 

The grow bed need comprise nothing more than a tray 6" - 12" deep.  I favour the shallow tray for a variety of reasons.  

 

The water enters the grow bed from one end.....you can set up a simple manifold to reduce the inflow velocity and to ensure that it is spread across the width of the bed.   At the outflow end, you just need to be able to adjust the depth of water in the grow bed.  I used a bulkhead fitting into which I screwed a one and a half inch male iron.  I used PVC pipe sections of various lengths to regulate the water depth.

 

For practical purposes, the water enters the grow bed at one end and flows along the length of the bed for draining from the overflow weir at the other end.

 

1. At what depth from the top of the surface would you place this pipe.  I understand it depends on the media, for discussion lets look at 3 (Sand, 3/4 gravel and clay pellets or hydrotron).

 

 

Set the manifold pipe up so that it is just below the media.  Even this is not essential.....it will just help prevent the build up of algae around the inflow to the bed.


2. Does the depth of the pipe matter if the depth of the grow bed changes?  From the above discussion a grow bed depth of 150 -300 mm is sufficient for most applications. So for this example 150 mm depth and 300 mm depth.

 

 

 

If we're talking about the inflow manifold pipe here, it doesn't matter at all.

 

3.  What flow rate should be used or does it matter?

 

All of my comments assume that you're using dedicated mechanical and biological filtration.....and that you can adjust the inflow to each bed.   In that event, flow rate can be highly variable.

 

Gary

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Thanks Gary, I was looking at your website and thought you would come to the rescue :)

 

 

 

you just need to be able to adjust the depth of water in the grow bed.

How do you determine the depth.  I know you mentioned the media choice and its wicking capabilities and I guess it would also depend on plants.  Do you have any rules of thumb for this?

 

Also would it be useful to have the manifold run the length of the GB allowing the solution to trickle down to the water depth and provide some aeration and create a slightly higher solution availability?

 

Thanks,

Clint

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Hi Clint,

 

Clay pebbles will wick up to six inches.....so, in a 6" bed, you only need about an inch to an inch and a half.

 

Gravel will only wick very slightly......so, in a 6" bed, you would run the water depth at about 2" to 3".

 

The difference is a bit more pronounced in a 12" deep bed......with clay pebbles.  Gravel remains the same.....it won't wick far at all.

 

In practice, you'll find that you'll use your spacers of varying lengths to set the water up were you want it.  When you first plant the bed out, it will be almost full of water for the first few days.....and you'll drop the level as the plant roots take hold.

 

Once the bed matures, you'll find that the roots of established plants will pull the water up a bit......so even seedlings are able to access it without too much difficulty.

 

It also depends a lot on what you're using these beds for.   It tends to be easier if you are operating on a all in/all out plant production mode.

 

If I was in your situation, I'll be using raft to grow your major production lines and wicking beds for almost everything else.   If you're messing with hybrid stuff in a commercial situation, you're going to get sick of it pretty quickly.....and it's a prospective point of failure from a water quality perspective, too.

 

Also would it be useful to have the manifold run the length of the GB allowing the solution to trickle down to the water depth and provide some aeration and create a slightly higher solution availability?

 

I wouldn't bother.  If you let the water flow in at one end - and drain at the other - all of the water has to make the same journey.  You don't want the water channelling......that's where you'll see anaerobic patches developing.

 

Gary

Edited by GaryD (see edit history)

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It also depends a lot on what you're using these beds for.   It tends to be easier if you are operating on a all in/all out plant production mode.

 

If I was in your situation, I'll be using raft to grow your major production lines and wicking beds for almost everything else.   If you're messing with hybrid stuff in a commercial situation, you're going to get sick of it pretty quickly.....and it's a prospective point of failure from a water quality perspective, too.

 

 

Thanks Gary. I hear you on the all in/all out production, I do that with my current media/worms beds and even that is a hassle.  You are correct about my situation I do 99% of my growing in the rafts as I grow manly leafy greens and such at the moment.  I was looking at a cf media/worm bed for a small demo system.  I am going to go with a FT, radial filter, bio filter, 150 mm media/worm bed and a dwc trough.  I will post some pics when I am done.  I am using Paul's DIY radial filter, looks dead simple. Got most of the materials today and plan to get at it tomorrow.  

 

I also like the wicking beds and that will be my next project, only so many clay balls in the air at one time, right Rupe?  LOL

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Rupe,

 

Clay balls are a peculiar thing.

 

Clay balls do have two things in common with crystal balls.....reproductive fallibility and a tendency for the details on their use to vary depending on who's doing the reading (and that will depend on a number of things including the proximity of prescription and/or recreational drugs.....or the phase of the moon).

 

Part of your confusion, Rupe, may be an issue of size.   All clay balls imported from overseas are landed in Brisbane.  All of the large ones are screened out and re-bagged and stamped "standard".....while all of the smaller ones are bagged up and stamped "large".....prior to transport to New South Wales.

 

Exactly the same thing happens with condoms, it seems.  No-one really knows why this happens.....but I've heard it has something to do with the state of origin (whatever that means).

 

How far from your clay balls does one find your wick, Rupe?

 

Gary

 

Clint......

 

Clay pebbles will wick up to six inches.....so, in a 6" bed, you only need about an inch to an inch and a half.

 

In light of representations from my colleague, I should revise that......clay pebbles in a six inch bed.....will wick about three inches.  With about an inch and a half of water in the bed, the media at the  surface will be pretty dry.

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Ok so I have a question then. If I’m using a 4.7 inch continuous flow grow bed 8 foot by 4 foot powered by an ibc tank with 40 tilapia. Should I run a filter separate as well. I’m using hydro stone (not the floating kind) but is still very light.  On top of the ibc tote is another 3foot by 3 foot grow bed. The combined plants is 3 pepper, 3 cucumber and 38 lettuce plants. 

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