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I've got the cut-off top of my IBC fish tank, to use as an extra grow bed. For plumbing reasons, it seems easiest just now to use it for a raft culture rather than a media-filled one.

Question is - what plants enjoy being on a raft?

I have some squash/pumpkin plants that need space somewhere, but I assume they are too big for a raft, or not?

Lettuces?

What else?

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I've done a couple tests of my small system and when running fish waste into media bed and then to dwc it doesn't filter out all the solids.  I just posted a new question about that here: http://community.theaquaponicsource.com/forum/topics/filter-after-s....  I was actually surprised how much it didn't remove.  

But I must say, it's probably because of how small my beds are.  If I had bigger media beds it would probably filter out much more.  

I remember hearing that putting aerators at the bottom of your raft tank causes water agitation that helps your plants take up nutrients better.

I've seen systems that add the aeration to DWC systems. That is why I was curious if, without aeration, there would be limitations on what kind of plants could be grown in DWC.

Alex Veidel said:

I remember hearing that putting aerators at the bottom of your raft tank causes water agitation that helps your plants take up nutrients better.

Adding air is a good thing but don't provide an air gap between your roots and the water. Keep the bottom of the net cup or whatever you are using submerged not the whole net cup just some of the bottom. 

@R.K. Castillo the small media bed could be the issue. I am pumping straight from the fish tank to my watercress bed which is pretty big and it drains straight to my lettuce raft system. My roots are clean and white. I also have an airstone placed every 4ft in my raft system. 

Oh, it had nothing to do with aeration, it was the actual disturbance of the water that caused the benefits.
That's correct, Alex. The agitation does more benefit to growth than the O2. Fish need 7 ppm plus, typically, for growth, while plant roots need only 1 ppm. So if you're fish are alive, your roots are fine. It is the agitation that keeps the gunk down that is the key, and there are other ways to agitate than bubbles (catfish in the GB, for instance). There are a lot if reasons to want DWC in the first place, and many variables to get there. Personally, I get much better results in DWC than any other method, with less work. Currently I am producing 4 1/2 heads of leafy greens per square foot per month, using a staggered planting schedule on 8" centers. That is tough to beat. The other advantage of rafts is mobility in troughs (though IBC's are doomed from the start...). I place my troughs right next to each other (eliminating walkways), and I can harvest all from one spot, even if the trough were hundreds of feet long. Anyway, back to the topic, I have had great growth with:
- all lettuce
- choi and other Asian greens
- kale and chard, though if you are harvesting leaves these become small trees better suited to media
- herbs: basil, thyme, oregano, tarragon, etc.
- mint, watercress (you can lift a raft and root prune to keep mint manageable)
- flowers
- strawberries +++

Big plants like tomatoes and cukes, etc., will grow in rafts, of course, but then mobility is lost, so they are also better suited to media. Arugula and cilantro I have had better growth in dirt than AP.

Sorry but agitation of the water doesn't have anything to do with keeping the gunk off your roots. That is false. I mean lets just think clearly hear for a second, if all it took was agitation of the roots to keep gunk off, why use filter systems, grow beds as filters, etc?

The aeration of your water from the movement at the waters surface from air stones and waterfalls does just that, Provide air/oxygen to your system. Having enough oxygen will also help avoid root rot because the nasties can't get a foot hold. What's really helping keep your roots clean besides the pre-filters and avoid root issues are all the beneficials in the water and the air/oxygen, not the agitation of your roots  in your Raft/DWC system.

You don't have to have a single air-stone under your raft if you choose not to,  just as long as your system has the correct amount of DO and pre-filters to keep the gunk out the DWC. You will have robust and nice white roots in your DWC. If you choose to grow tomatoes and cukes, etc. grow them in a raft. I'm not sure what mobility is being talked about but your are better off to grow that stuff in rafts. It's really up to you how you choose to grow them at the end of the day though :-)

Agitation does help keep roots clean... It's not up for debate at this point.

Good filtration is key but you'll never get 100% of the solids out...even using drum filters. Many of these micro particles have an opposite charge to that of the root surface and thus cling to it. As more particles pass by, the floc grows larger and larger as particles bind to each other and bacteria grows on the floculated mass. This interrupts the uptake of nutrients and several regulatory functions within the root mass.

In a static environment with no agitation (even with saturated DO) there is nothing to help this build up slough off of the root mass.

In an agitated environment, these masses (though the same physical amount) are broken up into smaller particles and remain within the water column but not fixed to the root mass allowing max nutrient uptake at the roots.

I don't know whether or not that helps with keeping gunk off of your roots, I don't have a dwc tank. But your logic doesn't add up. You're basically saying "simple solutions can't be the answer because someone would have thought of them already". Doesn't makes sense. Basically what the hydroponics market said about raising plants on fish waste: "it can't be that easy..." It would seem to me like people tend to over complicate things and it's rather common to have "face-palm" solutions appear and make everything better. Like adding redworms to your media beds. You know, people used to haul all their media out by hand, wash it all out and scoop it back into the grow bed. Adding a few worms was a pretty simple idea that solved a lot of problems. So, just because it's absurdly simple and hasn't been thought of, doesn't make it any less valid of an idea.

Like I said, I don't have a raft tank, I'm just regurgitating research. Got any other reasons why disturbing the water won't keep gunk off the roots?


Jason A. said:

Sorry but agitation of the water doesn't have anything to do with keeping the gunk off your roots. That is false. I mean lets just think clearly hear for a second, if all it took was agitation of the roots to keep gunk off, why use filter systems, grow beds as filters, etc?

It's not up for debate? I wasn't trying to debate...I'm telling you the information you are giving is wrong. I can get pictures of a system with airstones under the roots and a system without airstones under the roots. The roots are just as clean in the system without airstones as the system with airstones.  

Do you have any real world proof or just what you type?

I tell you what, you start you a system outside or inside and use chemical fertz add all the airstones you want under your roots and keep the water temps high like most do for warm water fish and I promise you your roots will be gunked up just like if you had an aquaponics system with no filtration and air stones in your DWC it will be something called root rot. 

When your done battling that and wasting money on your airstones to "keep the roots clean" you take that same outside or inside system, add your chemical fertz, keep the water temps high but this time make you a compost tea from worm castings and dump that in there, you don't need the airstones under your roots either you can have them in your sump or fish tank as long as you have enough DO. Guess what NO gunked roots and it's because of all the beneficials from the worm tea. 

Alex...I think you are lost or confused yourself. How did you become a moderator? I suggested something even simpler by not having to run airstones under your roots in DWC if you choose not to as long as you make sure you have enough DO in the entire system and you reply with all that?  

The airstones under your raft in DWC do nothing but agitate the surface of the water to provide more oxygen to your system, plants, fish, roots, beneficial bacteria, etc.

Tread lightly, Jason. You are in the minority here, and the other side of the fence, including myself, Ryan (who works with Rakocy and Leonard), and all of commecial APer's that I know of, are a strong force, and based on both logic and experience.

I am having a little trouble following your reasoning, so please help me. Do I have this straight?

-agitation does nothing to prevent gunk
-aeration does prevent gunk
-aeration does help under the roots, but only by adding O2
-filtration does prevent gunk
-filtration is all that is needed to prevent gunk
-white roots are healthy roots
-gunk on roots is also called root rot

Is that correct by your understanding?

If so, allow me to bring you back to square one. Gunk on roots of raft plants, as I define it, is bacteria, which may or may not have particulates stuck with it. Bioslime. Bioslime is not rootrot, nor is it anaerobic (per se), and it is abundant in highly aerobic and filtered conditions. It forms down flow of the filter, and is not stopped by filtering. I do not believe you have ever done aerated worm casting grows and had "white roots". My aerated casting brew is thick with chocolate slime on every surface, including roots when it is added to a system.

What caused me to consider agitation over aeration, were pictures of commercial raft systems where you can see where airstones are located in a raft by the better growth above. Ouroboros use air line diffusers, and you can see which side of the raft the line is on by topside growth. All the filtration, nutrients, and DO are the same in the entire trough, yet the bubbles cause the plants above them to excel. All the roots are white and clean, so if not for water agitation, Jason, why?

I grew two side by side, air-gap DWC strawberry troughs this spring. Water was pumped from one side to the other, and flowed back to the first by bridge siphon. Simple. That was the whole system. I had 7 bass on one side under the rafts, and none on the other. No airstones, no filter, no worries. The DO was always near saturation, and always the same on both sides. Initially, plant growth was identical, but over time the bed with bass did a little better, and the roots were clean and white, while the other side got dirtier and dirtier. The bass side also stayed spotless on the floor, and the other side accumulated sludge. Same aeration and DO, no filtration, the only diff was the agitation caused by the bass.

No worries man....I probably wont be posting anymore and will more than likely delete my account. I will reply to a few of your questions but this will probably be my last. Don't want to get on you guys bad sad obviously as you are well connected as you so clearly pointed out.Where did all these experts in aquaponics come from all of a sudden anyway, yet none of these experts are doing it on a LARGE scale, that I have seen anyway...if so please provide links. I am really interested. Also please don't send/post any links to these farms if they sell installation or consultation. Anyway......

-agitation does nothing to prevent gunk - No and I would have to say your example with the bass isn't that good. Yeah the stones and bass in the one side kept stuff stirred up and it was pumped into the other side with no where to go so it just stayed in there. Do you think you would have had the same results if fish and air stones were on both sides?  A better example would be leave your bass and airstones in one raft setup only and then take some pics of the roots. Do you think you would still have pristine white roots then?


-aeration does prevent gunk - No I didn't say that, I did say that the added aeration will help you keep root issues away because of the added air the nasties that might harm your roots can't survive but the beneficials can which help your roots in turn.


-aeration does help under the roots, but only by adding O2 - Yes from the exchange at the surface of the water when the water is being agitated/moved by the aeration. Still don't understand how you can say aeration helps keep your roots clean when the airstones themselves get dirty. So if they are blowing all that air out and still manage to get dirty....


-filtration does prevent gunk - YES


-filtration is all that is needed to prevent gunk-YES if buy gunk you mean your roots being coated in fish waste


-white roots are healthy roots-YES....please show me some pics of gunked up, slimy roots, brown slimy, etc. or what ever scientific words you prefer with big healthy plants on top. Granted some roots get a little stain to them but you can still call them white. I would/do


-gunk on roots is also called root rot....No I didn't say that, in my example I said you would have gunk on your roots which would be root rot in that scenerio. I don't think I said gunk on roots is also called root rot. Gunk on your roots could be many things not just root rot.

When you mention Bioslime I'm thinking you are talking about a slime that isn't really noticeable and also a slime that is benefecial to the roots for the most part. The slime I would be talking about is the nasty slime that inhibits root and plant growth. I have mixed a whole lot of worm casting tea and yes my roots are white or should I say may have a slight stain to them, no chocolate slime on anything. You might want to come up with some better brewing practices. 

Again it's not the stones under the roots. It's the benefit of the added oxygen from the exchange at the surface during agitation/water movement. You could put all those air stones in 55gal barrels and get the same growth.

You do realize in your example that one of your rafts was pretty much a settling tank right?

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