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GaryD

Aquaponics "Mythconceptions"

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Hi,

An article appeared in a recent aquaponics e-newsletter titled “Grow Beds used in Home Aquaponics Systems, how to get the best results.â€

In this post, I’ll dissect the article and demonstrate where I believe the information contained in it is problematic. I had to do it in two posts because the article was a bit windy.

The GROW BED is the multi function centre of the Home Aquaponics System.

The Grow Bed performs several very important tasks, and if we were to try and describe those functions in a simple way, one suitable description would be, it is a Bio-Filter in which we grow plants.

No problem so far.

A very happy and combination of duties. It is extremely convenient for our purposes, because as a Bio-Filter it collects and processes the ammonia and solid waste from the fish and returns the water to the fish tank clean, and by the growing of plants in the Bio-Filter (Grow Bed) we use up the nutrients and nitrates produced in the Bio-Filter (Grow Bed) producing excellent quality fresh veggies for our table.

While it’s been said before, it needs to be repeated as long as this misinformation continues…….it’s not the job of a bio-filter to collect and process solid wastes. As any trainee wastewater treatment operator knows, the efficiency of a bio-filter is impaired by solids loadings – the more solids, the greater the impact on nitrification.

Because the Grow Bed is such an important part of our total Aquaponics System we need to put some careful thought into it's design. Materials used, dimensions and location relative to the fish tank are all considerations.

We strongly recommend the use of 300mm (one foot) deep grow beds in your Aquaponics system. Beds with less depth and therefore volume, will also work, but not nearly as well.

The author of the article has little or no experience of grow beds that are less than 300mm…..but he does sell 300mm grow beds…….so, when he suggests that grow beds of less than 300mm “work, but not nearly as well†it’s fair to say that his “strong recommendation†is premised more on financial self-interest and less on experience or objective assessment.

The Grow Bed needs to be of such a length and breadth to provide sufficient surface area for the plants and together with depth provide sufficient total volume to be an effective Bio Filter.

Overall volume of a grow bed is an important factor. The more volume the total system has, the more stability in the system , particularly in temperature and pH.

Fish, plants, worms, beneficial bacteria and microbes all function better in a stable environment.

This stability has obvious flow on benefits for the health of the system inhabitants.

No one would disagree with the suggestion that fish, plants, worms, beneficial bacteria and microbes function better in a stable environment……but to suggest that the only way that can happen is in a grow bed of a particular shape or size is patently absurd.

In taking the decision to operate an Aquaponics system, we are desirous of producing the very best, healthy, nutrient rich and economical, plant and protein, for our family.

Aquaponics can deliver such produce by making use of natures wonderful interactive systems of worms, microbes and bacterium in a naturally balanced environment. It all works to its optimum when we provide it the best environment possible.

I totally agree.....but the most important environmental consideration is that of the fish since they drive the operation.

300mm (or more) deep grow beds will deliver optimum plant growth and health. They will provide optimum environment for the processing and delivery of nutrients to the plants, and the processing conversion of the ammonia given off by the fish, to nitrates.

In forming this opinion we have relied, not only on our own actual, very significant practical experience, but also on the experience of dozens of very experienced AP practitioners in Australia and around the world. Many of these people have accumulated a large body of experience in the use of 300mm deep (or deeper) grow beds as part of a well constructed Aquaponics system.

The fact is that there has been very little in the way of experimentation with grow beds of less than 300mm (in aquaponics anyway) so one would expect that, if the only grow beds that are available or recommended are 300mm ones, it would be logical that they are the ones that would proliferate.

Interestingly, grow beds of less than 300mm are much more widely used in the US where the development of aquaponics has taken a broader path.

All of these people report exceptional healthy plant and fish growth using systems based on the 300mm deep grow bed principle. There is now a large body of actual evidence that strongly shows that this is a good working principle/method.

This statement is a gross misrepresentation. Some of these people have killed all of their fish while others have killed some (which is reflective of the experience of the author of the article) and there is no evidence to suggest that their plant growth is any better for the simple fact of using 300mm grow beds.

All that can be said about 300mm grow beds is that they work (with which I’ve never had an argument) but any suggestion that they work better than anything else is pure conjecture.

We have manufactured and delivered many hundreds of complete AP kits based on the 300mm deep grow bed, and hundreds of 300mm deep grow beds to persons who are constructing DIY Aquaponics systems.

That’s more to the point.

The article continues in the following post.

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This is the second half of my dissection of an e-newsletter article - read my previous post first.

Flood and Drain:

Together with a 300mm (one foot) grow bed depth, we strongly recommend using flood and drain cycle and 20mm drainage gravel or similar in your grow beds.

Flood and drain water movement system ensures the even distribution of water, nutrients and air (oxygen) throughout the system. This provides multiple benefits.

By the use of this method, dry or nutrient and oxygen areas are prevented from forming in the grow bed.

Nothing less than 20mm (3/4â€) gravel should be used. This common gravel, by the way it rests together provides easy passage of water, solids, and worms throughout the bed.

As far as distribution of water, nutrients and air go, flood and drain is very good. A properly designed continuous flow system will, however, function just as well.

Gravel works well but is very heavy. Clay pebbles work well, too…..and, while much more expensive than gravel, they are much lighter on the back and hands.

Often folk cannot envisage plants growing in such a coarse media and they choose a finer media such as 5 or 10mm. This sized media will impede the action of the worms, the easy movement of solids and nutrients, and the Grow Bed will quickly suffer from partial or complete blockages.

Listed below are some of the reasons why 300mm or deeper grow beds are good....very, very good and highly recommended to deliver excellent results in your Aquaponics System.

…and there we go again with the 300mm thing……again.

Room for plant roots to develop and grow.

Some plant types such as lettuce do not require much depth (or nutrient) to grow successfully, but other garden plants such as tomato and corn, just to name two more common ones, do need depth space to put down good root systems. A given grow bed will have a variety of plants grown in it, so a grow bed depth bed depth that will accommodate a wide range of plant requirements is the way to go.

Plant roots in a flood and drain system proliferate in the way that they do….because they can….rather than because they should. The root mass of tomato plants is often mooted as evidence of the effectiveness of 300mm beds but the fact is that tomatoes produce different root mass according to the growing system in which they are being grown.

In NFT systems, for example, the root mass is much less than in a flood and drain grow bed but the capacity of NFT to grow tomatoes is no less than with F&D. If your goal is to grow tomatoes (rather then roots) then I’d suggest that you focus on other parameters (than grow bed depth) to ensure a bumper crop.

Depth and volume to process solid waste.

Solids passed by the fish, old roots, and other solid material is processed in the grow beds by those little wonder worms. Without going into detail here about the role of worms in AP, sufficient to say that the worms reduce solid waste by 60% or more and by their work and the action of flood and drain distribute the released minerals and nutrients throughout the grow bed/s.

300mm deep grow beds filled with 20mm drainage gravel with a good population of resident worms deliver an amazing plant growing habitat. (Not to mention excellent filtration for the fish tank.)

Worms play an important role in conventional flood and drain aquaponics systems in that they process the solids that do find their way into the grow beds. Without the worms, a conventional aquaponic system would become a prospective (fish) ‘killing field’ as the solids built up and the oxygen levels diminished.

In a properly designed system, they are useful (largely because they harvest dead bacteria and similar micro-organisms) but they are less visible…..and not so essential because the solids are removed (and are processed externally) before they get a chance to diminish water quality.

Bed Zones are established.

Surface or dry zone. --- The first 50mm is the light penetration and dry zone. Evaporation from the bed is minimised by the existence of a dry zone. Water waste minimisation is a very important principle in Aquaponics systems.

This dry zone also protects the plant base against collar rot. Additionally, by ensuring that this zone is kept dry, algae is prevented from forming on the surface of the grow bed media. Because this dry zone is present, moisture related plant diseases such as powdery mildew are minimised.

Seems reasonable enough…..although I doubt that light would penetrate through 50mm of most grow bed media.

Root zone. --- Most root growth and plant activity will occur in the next zone of approximately 150 - 200mm –in this zone, during the drain part of the flood and drain cycle, the water drains away completely, allowing for excellent and very efficient delivery of oxygen rich air to the roots, beneficial bacteria, soil microbes, and the resident earth/composting worms.

During the flood part of the cycle, the incoming water distributes moisture, nutrients and incoming solid fish waste particles throughout the growing zone. The worm population does most of its very important work in this zone, breaking down and reducing solid matter and thereby releasing nutrients and minerals to the system. Worm Teaâ€, as it is commonly known, will be evenly mixed and distributed during each flood and drain cycle. “Worm Tea†and the fish are entirely compatible, No possible harm can come to the fish by the distribution of this wonderful nutrient material throughout the Aquaponics System.

Here we’re still suggesting (against all technical evidence) that readers use the grow bed as an outhouse.

Solid collection and Mineralisation Zone

This is the bottom 50plus mm of the grow bed. In this zone fish waste solids and worm castings are finally collected.

The solid material has been reduced by up to 60% by volume, by the action of the resident garden/composting worms, and microbial action.

During each flood and drain cycle, what is left of the solids perkolates down into this zone

Further and final mineralisation occurs in this area via bacterial and earth worm activity. Due to the excellent action of the flood and drain cycle, this bottom area is kept “fresh†and vital by the excellent delivery of oxygen rich water during the flood cycle.

50mm of watery solids in the bottom of a grow bed would be anything but “fresh and vital†so the Solid Collection and Mineralisation Zone (as described) would be more appropriately called the “killing zone†……..because the build up of solid wastes would create anaerobic zones which would then deplete the system of oxygen.

As I’ve pointed out before, many fishkills are the result of a convergence of events (rather than a single cause) so anything which unnecessarily depletes oxygen levels should be avoided.

Some water storage occurs in this bottom zone.

Should the flood and drain cycle stop for any reason, such as a mains power outage, the bed will slowly drain down and leave approx 50mm of water at the bottom of the grow bed.

The stored water provides a safety buffer in the event of power outage or pump failure... This stored water ensures that the plants will survive for very long periods without water flow.

This means that we can simplify our safety backup system to circulate only the water in the fish tank, by the use of low wattage water pumps and/or aerators.

We can safely operate the system in backup mode (no main power supply) for very long periods of time–simply using an average size car battery as a power source.

This inbuilt water storage zone will supply the plants with water and nutrient should we need to isolate the fish tank for maintenance purposes, or treatment of the fish.

The 50mm water reservoir in the bottom of the grow bed might serve as a water source for deep-rooted plants in the event of a power failure but, because of the low wicking capacity of gravel would be no use to seedlings or plants with few/smaller roots.

Not only will most plants in such a grow bed not survive for “very long periods without water flow†- in hot weather they’ll drop like flies.

This article is representative of my concerns about the quality of information that is being provided (in some quarters) to existing and prospective aquaponicists.

In some cases it is incomplete (in that it fails to tell the full story) and in other respects it makes claims that are technically incorrect. In at least one instance, it makes a claim which is demonstrably untrue.

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The 300 mm depth seems sensible as a guide. Especially for new AP'ers.

I have never used a shallower growbed and don't think it would work well. Seems like commonsense really. Once most plants progress beyond being seedlings they send down roots. In my NFT pipe system, these roots form a "rootball" and also some plants send roots for metres through the pipe. Yes, some plants have very shallow root systems but I think 300mm is a good minimum depth to work from. I think a shallow GB say for tomatoes, cucumbers, pumkin or mint (some of the veges I grow) would be a disaster as the GB would be clogged with roots . . . like a root bound pot plant.

Likewise, I think flood and drain makes a lot of sense, despite the issues with getting bell siphons to work, once the do work it means the water is always emptying out regularly. I have tried contnuous flow and have ended up at times with waterlogged plants, root rot and smelly water.

Dave

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The root mass of tomato plants is often mooted as evidence of the effectiveness of 300mm beds but the fact is that tomatoes produce different root mass according to the growing system in which they are being grown.

In NFT systems, for example, the root mass is much less than in a flood and drain grow bed but the capacity of NFT to grow tomatoes is no less than with F&D. If your goal is to grow tomatoes (rather then roots) then I’d suggest that you focus on other parameters (than grow bed depth) to ensure a bumper crop.

I have to disagree with this Gary. I am not sure where you get the evidence of this "fact".

I think the reality is that a plant will adjust to its environment. In this case the grow bed or the pot or the soil in which it grows. I have grown tomatoes in growbeds (half barrel) and also in an NFT system. I have also grown tomato plants in foam vege. boxes in compost/soil mixture (less than 300mm depth) While each growing environment is different. Common sense again would dictate that the more depth or space the roots have, the more prolific will be the growth (given that each bed has enough nutrient)

I am not sure why you have focused so much on the 300mm depth issue. I know that a lot of people starting out in AP need some basic guidelines to help them get started. A lot of stuff I have learned by experimentation and of course by information from this forum and others. I have certainly appreciated being a part of this forum and have learned a lot. The thing I love about Aquaponics is that there are so many ways to end up with a good result. I am now regularly eating Barramundi of over 1kg and have grown veges to supplement our food supply at home. I have also encouraged a few others here in Brunei to try AP.

Dave

Dave

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Hi Dave,

The 300 mm depth seems sensible as a guide. Especially for new AP'ers.

I've never said that a 300mm grow bed wouldn't work well but rather that (for most purposes) shallower ones work just as well.....and that they offer some weight and cost advantages over 300mm ones.

I have never used a shallower growbed and don't think it would work well.

I've provided examples of where they do work.....just as well. One such example has been operating as long as any aquaponic system in Australia and it continues to operate today.

I think a shallow GB say for tomatoes, cucumbers, pumkin or mint (some of the veges I grow) would be a disaster as the GB would be clogged with roots . . . like a root bound pot plant.

As I've said previously, tomatoes grow well in NFT so they will grow satisfactorily in a shallow grow bed. In my view, growing pumpkins in an AP system probably amounts to a waste of grow bed space......and I'd recommend that people never grow mint in an AP system - the roots are too invasive.....regardless of the depth of grow bed.

Likewise, I think flood and drain makes a lot of sense, despite the issues with getting bell siphons to work, once the do work it means the water is always emptying out regularly.

I have tried contnuous flow and have ended up at times with waterlogged plants, root rot and smelly water.

I like flood and drain, too.....and I think that the narrow flow rate band in which they will operate has been resolved by innovative individuals like Affnan. Continuous flow can be done in either of two ways.....surface or sub-surface. Surface continuous flow is equal to flood and drain when it comes to aeration and (done properly) sub-surface is very good, too.

In a previous post (as you've indicated) I said....

"The root mass of tomato plants is often mooted as evidence of the effectiveness of 300mm beds but the fact is that tomatoes produce different root mass according to the growing system in which they are being grown.

In
NFT
systems, for example, the root mass is much less than in a flood and drain grow bed but the capacity of
NFT
to grow tomatoes is no less than with F&D. If your goal is to grow tomatoes (rather then roots) then I’d suggest that you focus on other parameters (than grow bed depth) to ensure a bumper crop."

have to disagree with this Gary. I am not sure where you get the evidence of this "fact".

I think the reality is that a plant will adjust to its environment. In this case the grow bed or the pot or the soil in which it grows. I have grown tomatoes in growbeds (half barrel) and also in an NFT system. I have also grown tomato plants in foam vege. boxes in compost/soil mixture (less than 300mm depth) While each growing environment is different. Common sense again would dictate that the more depth or space the roots have, the more prolific will be the growth (given that each bed has enough nutrient)

We appear to be saying the same thing.

I am not sure why you have focused so much on the 300mm depth issue.

I do so because one equipment supplier says that 300mm grow beds must be used while supporters of another one state that they are preferred.....for reasons that are simply incorrect or misleading.

I've simply countered the hype around 300mm grow beds and provided options for people who may not have access to them....or (more importantly) may not be able to afford them.

I know that a lot of people starting out in AP need some basic guidelines to help them get started.

In my view, they need accurate, detailed information.....and as you've indicated in your post, one of the really great things about AP is that there are so many ways to achieve a good outcome.

I have certainly appreciated being a part of this forum and have learned a lot.

And I, and our other members, enjoy and appreciate your contribution.

It's alway great to hear from you, Dave.

Gary

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I've simply countered the hype around 300mm grow beds

I think its more like you are creating hype around 300mm grow beds. As an AP forum we should be encouraging people to use 300mm and deeper. Creating a safer standard that will help minimize failure. It does not make sence to attack a safe standard. Its like telling people to not use training wheels on there kids bikes. Some of those kids with bruised knees will stop riding there bikes.

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Hi Dufflight,

Its like telling people to not use training wheels on there kids bikes. Some of those kids with bruised knees will stop riding there bikes.

Your analogy is a useful one but probably not for the reasons you suggest.

Every day, the list of people who have killed fish (because of misleading, incomplete, simplistic and self-serving advice) grows longer and longer.

What's clever about telling someone to do something a particular way when they could achieve a similar result for half the money?

Gary

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What's clever about telling someone to do something a particular way when they could achieve a similar result for half the money?

Gary

Easy, if you tell people they can do it with 150mm gb running continuous flow and they don't have enough bacteria working and the gb clogs up and they end up with dead fish. And because they have limited there choice to 150mm they can't add more media so they have wasted more money. Its clever to incourage them to set up a stable safe and tested system to start with.

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I've demonstrated how there are people who are already achieving everything you suggest for half the investment.....and have been doing so for longer than most of us have been involved in aquaponics.

I think the discussion has become circular.....and is no longer achieving anything.

I suggest that, if you have nothing new to contribute to this thread, you direct your attentions to other matters.

Gary

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I've demonstrated how there are people who are already achieving everything you suggest for half the investment....

Yes, 1 place is doing it. Why should it be pushed here. I'm not the only one that keeps circling back to this.

I suggest that, if you have nothing new to contribute to this thread, you direct your attentions to other matters.

Gary

I just think if shallow gb's are to be pushed at least put a warning that the gb's that are used should be the kind that can be filled to a higher level. So after the first lot of fish die the people can still add more media without having to shell out for new deeper gb's.

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Yes, 1 place is doing it. Why should it be pushed here.

Because I'm more than happy to showcase successful examples of aquaponics (particularly when they save people money)....and exploring the widest range of useful options is in the interests aquaponics.

Gary

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Gary, just out of interest sake (and this may have been answered earlier, sorry if I missed it but...) are you removing solids before it flows into your shallow beds?

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Gary,

One thing you haven't mentioned (as far as I am aware) is the problem of algae where the medium is exposed to sunlight. Before I continue let me state that I have recently measured my growbeds depth and all are less than 300 mm. 299 mm in fact! (joke) So that means I am APPC on this forum at least.

Seriously though, if water levels reach the top surface of the media, algae can form, in the tropics, even when not directly exposed to sunlight but indirect light.

It would seem that your shallow grow beds (from your posted photo) are actually NFT channels filled with media (aggregate) and therefore you are not running a flood and drain system but a trickle of water well below the surface of the media.

Until I saw your photo, I assumed your 300mm arguments were about grow beds and not channels. The glaringly obvious problem for me was the very small volume of water that would fill a shallow tub (growbed) and the problem of flood and drain, root depth (many veges require deeper depths to do well) and anchorage of plants etc.

Also you have said that mint should not be grown in an AP system. I have been growing mint now for over two years and have had no problems with roots clogging the pipe. I use a stormwater pipe blocked at both ends with a slot cut in the middle. I think it is about 50 cm diameter. I will post a photo later. The mint cascades over the pipe and we always have a good supply these days.

I would not grow mint in a shallow grow bed of less than 300mm. (In your channel system I may have a chance) Can you see my point here? You have told people that you can't/shouldn't grow mint in AP systems. Likewise my pumpkin crop has flourished this year. Pumpkins obviously grow outside the growbed but the roots start in the growbed. Yes, I do have to clear roots out of the bell siphon on a fortnightly basis but it works.

That is my point. I think a lot of people are doing Aquaponics as I am, making use of bathtubs, recycling PVC pipe offcuts from building sites, salvaging old car batteries for backup DC pumps and so on. I have never bought a commercial AP system and probably never will because I can't afford it. Learning by experimentation can kill fish, granted, but the way you do AP may be very different to the way other people do it, as long as we can make it work and produce healthy food. Isn't that the point?

Dave

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Hi Dave,

I don't know where you got the impression that I grow anything in NFT channels. My own systems have been largely based on 300mm deep grow beds......simply because I couldn't get anything less in fibreglass.

The photo link that I provided does feature some NFT trough but the black plastic grow trays were what I was referring to......as in the videos.

That is my point. I think a lot of people are doing Aquaponics as I am, making use of bathtubs, recycling PVC pipe offcuts from building sites, salvaging old car batteries for backup DC pumps and so on. I have never bought a commercial AP system and probably never will because I can't afford it. Learning by experimentation can kill fish, granted, but the way you do AP may be very different to the way other people do it, as long as we can make it work and produce healthy food. Isn't that the point?

I'm totally supportive of people of using recycled materials.....and of doing things in different ways (notwithstanding the criticism that I take for it)..... and that is definitely the point.

Gary

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Sorry Gary, I am a bit confused now because I see that you have a stack of NFT channels in a photo captioned "treasures" on another post. The ones next to your shed. Perhaps what you mean is that you haven't grown anything in them yet.

I've been to a few Hydro farms here and they use similar sized channels for growing lettuce. No medium of course, the lettuce are suported by foam. Some hydro farms here also use the styro foam floating raft system.

I will try and post a photo of my big pipe in which I grow mint, tomorrow. I suppose it is more or less a hybrid of a NFT and a flood and drain growbed as I am only trickle feeding it, continuous flow. It is enough to keep the mint very happy but other plants no longer grow in it as the top layer of gravel is usually quite dry.

Your Queenslander growbed trays look huge and shallow. I think good for lettuce and other shallow root crops. If I had a greenhouse here I could use them. I'm still wondering though why bother with gravel/clay pellets with your clean water and shalow beds, why not convert to floating raft or NFT and save on using medium altogether?

Dave

Dave

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Hi Dave,

Sorry Gary, I am a bit confused now because I see that you have a stack of NFT channels in a photo captioned "treasures" on another post. The ones next to your shed. Perhaps what you mean is that you haven't grown anything in them yet.

Oh......I thought you were referring to the photos that I posted that featured the shallow grow beds. The little "treasure" system is something that I've had for a long time......it will accommodate 48 plants. It features in various posts that I've made over the past 2 - 3 years. While it is not my favourite growing system, it may still find a use in my new Queenslander unit since the water quality will suit it better than my previous conventional AP systems.

I will try and post a photo of my big pipe in which I grow mint, tomorrow. I suppose it is more or less a hybrid of a NFT and a flood and drain growbed as I am only trickle feeding it, continuous flow. It is enough to keep the mint very happy but other plants no longer grow in it as the top layer of gravel is usually quite dry.

As I said in a previous post, I wouldn't plant mint in any AP system. I can't recall seeing a plant with a more aggressive root system.....it had chased up through the pipework and eventually caused blockages everywhere.

Your Queenslander growbed trays look huge and shallow. I think good for lettuce and other shallow root crops.

They're actually 1950mm long, 1300mm wide......and 300mm deep. They were originally sized so that a Styrofoam raft could be used in them without having to trim the sides.

Had I been able to buy shallower fibreglass grow beds, I would have done so. As it is, I may just limit the depth of the clay pebble media to 150mm.

If I had a greenhouse here I could use them. I'm still wondering though why bother with gravel/clay pellets with your clean water and shalow beds, why not convert to floating raft or NFT and save on using medium altogether?

All aquaponics growing systems are good......and no one system is ideally suited to every type of plant. I prefer to have a bit of everything.

Gary

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Gary,

One thing you haven't mentioned (as far as I am aware) is the problem of algae where the medium is exposed to sunlight. Before I continue let me state that I have recently measured my growbeds depth and all are less than 300 mm. 299 mm in fact! (joke) So that means I am APPC on this forum at least.

Dave

After reading your post, I measure my growbeds in my indoor system that grew peppers, tomatoes, basil, lettuce, green onions, swiss chard. While the container is 400 millimeters deep, the depth of the media I have used for over a year to grow the above is only 120 mm. NO root problems, blockage problems or problems growing 4 ft high tomato plants.

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[quote name=GaryD;19308

As I said in a previous post' date=' I wouldn't plant mint in any AP system. I can't recall seeing a plant with a more aggressive root system.....it had chased up through the pipework and eventually caused blockages everywhere.[/color']

Gary

Hi Gary,

Here are some photos of my "big pipe" growbed, sucessfully growing mint without the agressive root growth you describe. In fact agressive root growth is not such a problem. I deal with it with tomatoes, pumpkins and cucumbers.

It is just a matter of having growbeds big enough or deep enough to allow the plant to grow and also providing pipes (I use 40mm mostly) that can easily be cleared of wandering roots. It also helps to have a bell siphon outer pipe big enough to each in and clear the roots that head toward the fish tank.

Dave

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I have posted three photos. Two are of a 1000 litre tank where I keep Tilapia and Barramundi. One photo with air pump on and the other with air off. As you can see water quality is good. I have a big pump in the centre of the tank that sucks out solid waste. The water is pumped into a 200 litre grey drum which is a swirl filter and biofilter. From this filter, water gravity feeds to 2 250 litre gravel/clay growbeds. There would be around 250 - 300mm of gravel I think but hey? who's measuring?

On the other side, I have a small aquarium pump that pumps water to the big pipe. It is now pretty much continuous flow, previously I used a bigger pump as it is fitted with a bell siphon.

The whole system can be seen in the background of the photo in my previous post.

It is all a great learning experience and I judge my success by the fact that I have now achieved my goals of being able to produce a regular supply of fish for my family and also growing enough mint to make a tabouleh salad whenever we want to.

Note: Mint is expensive and hard to find here in Brunei. Supermarkets have it in small quantities and it is difficult to grow in soil (I've tried) Have never had to clean roots out of the big pipe and it has never got clogged up.

Dave

PS The barra pictured is one of six that I filleted and BBQ'd for lunch with friends. I also BBQ'd two nice big Tilapia (whole) each was around 1.5 - 2 kg.

All my systems are home made with the exception of course of the plastic tanks and other hardware. I have learned a lot from this forum and thanks to Murray, Gary and other active members of both forums for their information and ideas. We are all doing it differently in our own way and if it works and produces healthy fish and vegetables then it is an enormously satisfying hobby.

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Yep FF hang about I'll have to search the pics on my Mac.

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OK here they are... shows internals. Note the price of a laundry basket in Brunei. The white stuff in centre is coral in a laundry bag. I also add aquarium foam around the sides. It works well. Total cost under $50.

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On the second one I made the drain hole is in the middle. 40 mm pipe and ball valve to dump solids every day or so. It is very effective but you need to get the drum up nice and high on a tank stand of some kind. I used hardwood. Gravity feeds to GB's. Foam bio filter at top can be washed with the hose to clean. I do this maybe every 4 weeks or so. Some fine solids get trapped by the foam. Coral helps to buffer pH I think and provide more surface area for bio film (is this right Gary?) Anyway it works and haven't killed a fish for ages!!!

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