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What are your thoughts on system design?  Media vs raft.  Deep media beds vs shallow.  Siphons vs timers.  Tell us your thoughts and let's get the conversation rolling

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Hello,
I don't think a raft system has to have a clarifier, it just has to have the solids removed, which could be done with with a good filter. Also, why does the raft system need to be cleaned every day? Is it because it acts like a clarifier, or were you refering to cleaning the clarifier every day?

Is any aquaponics system designed for growing subterranians?

Why are raft systems not very good for long term crops? Is it because the nutrient levels change more rapidly, where in a media based system the nutrient levels are more steady because they build up in the media?

Thank! These are genuine questions. I hope they don't seem condescending.

David
By the way, I just went to BackyardAquapoincs.com and it is a good website. There is a lot of good information there.

Sylvia - I am curious why you started this network if you already work with Backyard Aquaponics? Do you feel as if there is something lacking there?

David
Hi David,

Solids are typically removed from raft systems using a clarifier, but you are right - any filter that removes the solids would do it. I was referring to cleaning the clarifier. You can absolutely grow subterraneans in a media system - Travis Hughey was telling me yesterday that he has grown onions and potatoes, and I've grown carrots.

You will find that that there isn't a tremendous amount of research based answers in aquaponics yet, but I can tell you that the reigning theory about growing longer term crops in media is that the more intensive bacteria base in the media ends up breaking down the solids and providing the micro-nutrients needed by longer term plants. But just a theory. I've just never heard of indeterminate tomato plants, etc. being grown in a raft - typically only greens and herbs.

I love your curiosity. No condescension sensed at all - just good, probing questions
It is an excellent source of information and I recommend it often. I started this network because I felt that there really weren't great options for US focused aquaponics discussion, and the Backyard site can be intimidating to some newcomers - there is just so much information. I also love the Ning format with photos, video, etc. I don't really work with them, just have gotten to know Joel a bit and try to support good people doing good work in aquaponics whenever I can - this is a very small community ;-)

I'm going to punt here a bit and send you to a recent blog post I did on this very subject - http://aquaponicgardening.wordpress.com/2010/02/17/aquaponics-commu....

Take care,

Sylvia
Sylvia,
That is so funny. I didn't realize that you had written that article. That was actually the article that made me end up at this site. My mother forwarded me the article from the NY Times, I ended up at your blog, and then I ended up here.

I am almost certain that the doctor down in the UVI said somwhere is his chapter in Recirculating Aquaculture that he had grown larger plants in his raft system, but I am not at home right now, so I can't check on that.

I would imagine that if you have a cone shaped clarifier it would be tremendously easy to remove the solids. However, I am not willing to spring for one at this time since I am not actually buildling my own system, but a system for a friend.

The raft system initially appealed to me because my education focused on waste water treatment, so the raft system made the most sense to me. Treat the water one stage at a time. Clarifier, folowed by a mechanical filter, followed by a biological filter.

If there is ever a way I can help out with this new community, just let me know. I am a civil engineer by training, a residential construction worker by trade, and a hobby artist. I hope to start construction on my friend's system next Saturday, if the weather is good.

David
First: all the numbers and calculations necessary to design your system are available, but they are scattered all over the Internet. During my study I have tried to assemble them in an Excel sheet. I enclose the sheet, but use at your own risk and read the papers that led to the calculators, it will give you lots of insight.

As for design, I am under the impression that a lot of possibilities are overlooked and older systems are forgotten.
Existing systems seem to be considered as end of design.

I like to think out of the box. That is the subject of this thread.
I aim for energy conservation and simplification. To reach that, I am not afraid to first think complicated, then I keep the good parts and try to simplify.
Let me fire my ideas on you and please comment.

30 years ago, I had a big aquarium with a bottom (under gravel) filter. A pump circulated the water. I don't remember the filter ever clogging, but I might have forgotten.
that thought raised the questions:
1. why is it that in raft aquaponics fish are not grown under the rafts?
After all, there is where lies the biggest water body in the system.
Or in between rows of rafts, i.e. in long cages? This would keep the fish away from plant roots if that forms a problem, and make harvesting easy.
Fish densities overall would be much lower.
Even if the gravel would tend to clog, there are vacuum systems that allow the gravel to be cleaned, either directly in the water, or outside, in a filter system.
or an array of drainage pipes would allow to pump out most of the solids, (settling and floating) to a filter
2. rafts are used because they float, but the problem with them is they cover the water surface and impede oxygen exchange, this on the largest exchange surface in the system.
result: much more aeration needed, much higher energy consumption.
Easy to solve by using floats and grating to support the plants.
3. another problem with rafts is plant roots permanently in the water. It is one of the advantages of ebb and flow in grow beds
Solution: use hollow floats that keep the plants just above water level, i.e. standing on longintudinal racks.
These racks can serve as separation of the rows and form the sides of the long cages.
at regular intervals, pump air in the floats, the roots are lifted out of the water, are thoroughly aerated.
let the air escape, the roots are lowered and in turn aerate the water.
Ebb and flow turned upside down. Perfectly adjustable to different plant needs and stadia.
Cheapest would be long inflatable tubes.
hollow bottomed floats with solid sides would favourise oxygen exchange as the pressure on the air increases.

extra advantage of this system: a square tank is cheaper to build than a long narrow one

that's about it, for now
Frank
forgot to add the file
here it is
frank
Attachments:
Main reason not to have the raft tanks and fish tanks combined has to do with the solids building up on the roots and impeding oxygen exchange for the roots with the water.
Also, makes it hard to see the fish and feed the fish without disturbing the plants.
The raft tanks don't need to be especially deep while the fish do a bit better with deeper tanks. Having the added water volume of the raft tanks does improve the system stability an improve quality for the fish even if the fish don't have physical access to the space where that extra water is.
TCLynx said:
Main reason not to have the raft tanks and fish tanks combined has to do with the solids building up on the roots and impeding oxygen exchange for the roots with the water.
Also, makes it hard to see the fish and feed the fish without disturbing the plants.
The raft tanks don't need to be especially deep while the fish do a bit better with deeper tanks. Having the added water volume of the raft tanks does improve the system stability an improve quality for the fish even if the fish don't have physical access to the space where that extra water is.

Would have thought the requirement for sufficient volume/depth of water for the fish would have been self evident...

Typically, raft beds are 12" deep or more recently...less... likewise, they're often only 2' wide...

This would severly restrict the number of fish that could physically fit within a raft bed.. with any degree of wellbeing...

Besides the fact, that having fish would be continually stirring up any solids materials... exacerbating potential problems with them clinging to roots... they would also be consuming oxygen from the water... in direct competition to any plant and bacterial requirements...

You could combat the oxygen requirement... by a degree of increased flow... and/or added pumped aeration... but this adds complexity and cost...

For the sake of feeding, monitoring, harvesting, oxygenation requirements... and general well being...

I wouldn't recommend placing fish into the beds of a raft system....

And I've not seen anyone yet.. that has extolled the virtues of having gravel, as an "under-gravel filter"... or any other reason... in an aquaponic system, media or raft based ....

Those that have tried it though... have universally condemned it ... as either a "pain" due the requirement to continually clean it... or as "bad idea", because it caused fish deaths due to bad water parameters resulting from rotting uneaten feed and wastes becoming anerobic...
I started another discussion that lists the functions of the flood and drain media beds as this discussion could get really long.

A few points I'll address here though. Media

Lava rock, cinder or what our aussie friends call scoria is commonly used. It is kinda hard on the hands to dig in so I mostly only used larger chunks of it around my drain stand pipes to help hold the smaller river gravel back but it does provide great surface area and useful trace elements. It is more fragile than many other types of gravel so be gentle while washing it (I wouldn't use a cement mixer to wash it.) I personally like the brown river pebbles of under 1/2" size. They are smooth and heavy but fairly easy to dig in and the cheapest pH neutral stuff I can get here.

I do advise you do some pH testing about your planned media before buying truck loads of it. Read my tips about tap water before simply assuming that your tap water is the pH it is right when you fill a container. It might be worth picking up a gallon of distilled water to run your pH tests with the cinder. The high potassium content looks promising. Potassium and Iron are the most commonly lacking nutrients in aquaponics (Iron mostly due to high pH in some systems though.)

If you use pH buffering media as your grow bed media. Adding acid won't change your pH long term, you will just bounce things. My system is 40% filled with shells My pH is strongly buffered to resist going below 7.6. The only time my system tend below that is when I'm maxed out on fish load and the bacteria are working full tilt and using up carbon at an alarming rate. I have seen pH as low as 7 in a buffered system but lessen the load and the pH is back up to 7.6. All that is to say, if you mistakenly use limestone as your media, you can't adjust the pH below that which the limestone buffers. Your choices will be to either replace the media or get used to only growing plants that like the high pH.

I think I will start a separate discussion that can list numbers and rules of thumb for system design. I can add numbers for the media based designs, hopefully others can share what is needed for raft systems.
I had considered floating a raft on top of my aquarium, but quickly realized that wouldn't work so well. See, mine is indoors and I am highly dependent upon my aquarium hoods to keep the water in my tank (I live in the desert, so this is important), and to get adequate lighting into the tank. The room my system is in faces South and the street, and there's an olive tree out there that blocks sunlight from getting in. That's even without my paranoid tendencies to keep all my windows' blinds down so random strangers don't see in ;)

If my system were outdoors (which I might do one on my patio), I would go that route, actually. I know there's an issue of "sludge," but I've never experienced that with my flower growing small systems. Think of those betta vases that have the plastic cup and a lilly sitting on top. Those are basically decorative mini hydroponic systems.

I saw a YouTube video of the NYC Science Barge. It has an on-board hydroponic greenhouse and they were beginning to get into aquaponics. They utilized the floating raft system on top of a huge tube with ample surface area. They also had a really ide of how to feed worms to your fish. I'll have to find the URL and a follow-up on how that worked.
Frank,

Welcome to the community and thanks for posting these "out of the raft" ideas. Part of the benefit of a forum like this is starting interesting discussions and exploring new ideas.

Frank De Block-Burij said:
First: all the numbers and calculations necessary to design your system are available, but they are scattered all over the Internet. During my study I have tried to assemble them in an Excel sheet. I enclose the sheet, but use at your own risk and read the papers that led to the calculators, it will give you lots of insight.

As for design, I am under the impression that a lot of possibilities are overlooked and older systems are forgotten.
Existing systems seem to be considered as end of design.

I like to think out of the box. That is the subject of this thread.
I aim for energy conservation and simplification. To reach that, I am not afraid to first think complicated, then I keep the good parts and try to simplify.
Let me fire my ideas on you and please comment.

30 years ago, I had a big aquarium with a bottom (under gravel) filter. A pump circulated the water. I don't remember the filter ever clogging, but I might have forgotten.
that thought raised the questions:
1. why is it that in raft aquaponics fish are not grown under the rafts?
After all, there is where lies the biggest water body in the system.
Or in between rows of rafts, i.e. in long cages? This would keep the fish away from plant roots if that forms a problem, and make harvesting easy.
Fish densities overall would be much lower.
Even if the gravel would tend to clog, there are vacuum systems that allow the gravel to be cleaned, either directly in the water, or outside, in a filter system.
or an array of drainage pipes would allow to pump out most of the solids, (settling and floating) to a filter
2. rafts are used because they float, but the problem with them is they cover the water surface and impede oxygen exchange, this on the largest exchange surface in the system.
result: much more aeration needed, much higher energy consumption.
Easy to solve by using floats and grating to support the plants.
3. another problem with rafts is plant roots permanently in the water. It is one of the advantages of ebb and flow in grow beds
Solution: use hollow floats that keep the plants just above water level, i.e. standing on longintudinal racks.
These racks can serve as separation of the rows and form the sides of the long cages.
at regular intervals, pump air in the floats, the roots are lifted out of the water, are thoroughly aerated.
let the air escape, the roots are lowered and in turn aerate the water.
Ebb and flow turned upside down. Perfectly adjustable to different plant needs and stadia.
Cheapest would be long inflatable tubes.
hollow bottomed floats with solid sides would favourise oxygen exchange as the pressure on the air increases.

extra advantage of this system: a square tank is cheaper to build than a long narrow one

that's about it, for now
Frank

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