Hybrid Aquaponics – The Marriage of Media and Raft

Raft Aquaponics

Image Credit: Green Acre Aquaponics

The substantial difference between media and raft-based systems jumped out at me when I first became involved in aquaponics (AP) in early 2009. I quickly saw that media-based systems are best for homes and schools because they are simple to design and operate, require no solids removal, and can grow just about anything.   Raft-based systems, on the other hand, are more appropriate for commercial applications because they are best suited to grow leafy greens, can be more heavily stocked with fish, and because they must include a solids removal component, they require a more sophisticated system design and more diligent maintenance.

Then, a couple of years ago, my AP world was rocked when I learned about hybrid aquaponics systems.  Just as aquaponics itself blends the best of hydroponics and aquaculture and solves some of their problems, hybrid aquaponics blends the best of media-based AP(low maintenance and the ability to grow fruiting plants) with raft-based AP (better growth of leafy greens) in a way that solves the biggest problem of raft systems (solids removal).

Late last year, we challenged Matt, one of our “aqua-engineers”, to integrate Raft Beds (along with a simple fine solids filtration system) into our AquaBundance Modular design schema.  Matt has spent the past nine months designing, testing and honing this system and this month we are ready to release it!

Here are a series of FAQs designed to help you understand our AquaBundance Raft Beds, why they could be a valuable part of your aquaponics system, and what makes our design unique in the aquaponics industry.

Why Grow With Rafts?

Hybrid AquaponicsWhile most plants will grow in both media-based and raft-based aquaponics systems, many plants have a favorite aquaponic style.  Media-based systems are absolutely the best environment for growing larger, fruiting plants.  Why? Because as solid fish waste breaks down in media-based grow beds, it releases the full range of nutrients that flowering plants require for all stages of their growth. And these nutrients are typically available at a much higher levels in media-based systems (raft-based systems by design filter out and remove the solid waste). Plus the media in media-based beds provides structure for the plant roots to grab hold of which in turn provides the essential support needed for both taller and larger plants.

Raft beds, however, excel at growing leafy greens such as lettuces and braising greens.  While these types of plants will grow just fine in a media bed, they will grow faster, bigger, and be significantly easier to harvest out of a raft since there is no media to pull out of the roots.  The downsides, however, are that raft systems typically have significantly lower nutrient levels over all and they require that the fish solid waste be extracted from the system so it doesn’t coat the roots of the plants and starve them of oxygen.

A system that combines the productivity of both of these growing techniques and solves the filtration problem, can offer the grower the most productive system possible!

I thought hybrid aquaponics systems didn’t need any solids filtration?

Bucket FilterThat isn’t entirely true.  The first “gross” level of solids filtration is accomplished through mechanical trapping of waste in the grow beds (which the bacteria and red composting worms then convert to plant food).  However, our testing has shown that in combined media and raft-based systems some fine solid waste is still lurks in the water.   We were concerned that this material might coat some plant roots…especially those that take longer to be harvest-ready like braising greens and basil.  That is why we developed our Bucket Filter.  This simple filtration device traps most of the remaining solid waste before it enters your Raft Bed(s).

How much maintenance does your Bucket filtration system require?

Our Bucket Filtration system requires just a few minutes a week to maintain.  That is right…you heard me correctly.  All you need to do is open the lid, remove the filter and rinse it with a hose once a week.  One of competitors admits that their systems take up to an hour a day of maintenance.  We’re betting you would rather spend that time starting new seeds, admiring your fish and harvesting all your produce!

Why did you opt for sizing the holes in the raft for grow plugs versus the traditional 2” net pots?

We did this for a few reasons.  First, we develop systems for busy home-owners and teachers and we assume that you value your time as much as we value ours.  The traditional method of starting seeds in growing media and then transferring those to net pots just doesn’t make sense to us.  We think it is much more efficient to start the seeds in the plugs (Rapid Rooter, Oasis Cubes, Rockwool cubes, etc.) and place those plugs straight into the raft itself.  Plus, this prevents making the mess in the bottom of most raft systems as planting mix is sloughed off into the water.

But if you don’t agree with us and would rather use baskets, no problem!  You can drill your holes larger with a 2” hole saw any time you want.

Do I have to arrange my system so my raft bed(s) is(are) right after my media beds?

Hybrid Aquaponics multiNo, you don’t!  That is the beauty of our system design.  The sump tanks are the central mixing point for all the water.  Your water will enter your Bucket Filter directly from the sump tank just like all your other grow beds.  The only placement rules are that the raft beds need to be level, and if you have more than one, they should all be either at the same height or each one slightly lower than the one next closest to the bucket filter.  This is because the water slowly flows from one to the other via gravity.

We think the biggest advantage of our design flexibility is that now you can place your rafts where they will grow your plants the best….perhaps in the back of the greenhouse where they will get more filtered and less direct sunlight.

I thought raft beds needed to be on the ground?

Again, we are happily rebelling against tradition. We have designed our raft beds to provide the same waist high level of comfort as the rest of our grow beds.   There is just no good reason to put these beds on the ground, unless you really enjoy stooping and squatting.  And if you do, just make sure your raft beds are higher than the top of the sump tank so they can drain back into the sump via  (you guessed it!) gravity.

19 thoughts on “Hybrid Aquaponics – The Marriage of Media and Raft

  1. Hi Sylvia, I would love to know more about the bucket filter between fish tank and raft beds. Could you tell me more, how to make this filter myself? Or is there a specific design I could follow? Is this what you would call a “swirl filter”?

    Thanks!

  2. Sylvia I had sort of the same idea. I attached my floating raft bed to the grow bed drains. The water flows from my grow bed through the raft beds back to my fish tank. The lettuce I planted is still getting the roots all mucky which slows growth down.

  3. This is how the Aztec and Mayan indians did it.. they would weave beds of debris the make a mat out of dead vegetation then pack mud and dirt on top of it for the grow bed.. then float the beds in canal’s

  4. How high do you have the media piled underneath your rafts? I am doing a similar hybrid system at home but with no raft on top. I just stuck some net pots in the media and made sure that there is a 2″ dry layer at the top. The water just constantly flows through my media, and there are no open “channels” of water. Does your system still have an open channel at the top, just a more shallow one than DWC? Does your system run continuously or on a timer cycle? Thanks!!

  5. I have to disagree with some of your suppositions about media-based systems, based on my extensive research of McMurtry’s system at NC State. It’s as if people think they are breaking new ground here, but it’s been extensively practiced on a commercial scale, growing greens and fruiting intercropped together, now there are even more options. So, I have to say that hybrid systems are a step in the direction of complete media-based commercial systems. Of course you can disagree but maybe we’ll have a chance to prove it side by side.

  6. Pingback: Hybrid Aquaponics – The Marriage of Media and Raft | Green Energy Approach

  7. i am just getting ready to build my first system, i have been looking at different videos for a year, the hybrid is the way i am going,
    do i put the swirl filter between the grow beds and the rafts

    plan is to have fish tank overflow into grow beds with auto siphons, grow beds drain into swirl, drain into rafts, which drain into sump, pump up to fish tank

  8. Pingback: Hybrid raft + media? | Jeff Prentice

  9. The idea of sounds good and can work on small scale but if you are designing a 30 UVI system the will require around 350 tons of fish feed a year what media will handle that? Can you imagine this quantity? I would say you would still need most of the solids to be removed and use part of it for the grow bed.
    if you need to concentrate the nutrient you can do that look at Dr. Savidov design ( yes it is complicated and very expensive system that i don’t see myself using it as whole but i would use the part in need like the nutrient concentration and return it back to the system, still i can benefit from having the solid for Biogas and compost.

  10. The media-based method has been done large-scale and long term at least twice. At a fraction of the cost per square foot. The hybrid system is a transition to 100% media based, in my opinion.

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