A Community and Forum For Aquaponic Gardeners

Pump in DWT - raft/sump

I've been designing a hybrid system for some time now combining media beds with DWT and nft and i am starting to see some surprising benefits. My plan is to let the f&d media beds flood into the DWT so that the rafts rise and fall with the fluctuating water levels. With the DWT having so much more volume than the media beds, the water level would not change too drastically.

I've read a lot of posts about the challenges of getting enough oxygen to plants in rafts and I'm now fairly convinced that the way to go is to install a lip along the inside length of the trough such that the rafts cannot sink down below a minimum height. This way, when the water drops because it is filling media beds the rafts will be suspended and the upper portion of the roots exposed temporarily to air. This regular action would bring oxygen directly to all of the DWT plants without the use of any air pump at all!

Additionally, this makes it possible to mount the DWT plants into something other than a styrofoam raft. Although one big bonus to the foam is that it is great at insulating the water in the trough.

I'm going to give this approach a try on my new system. It should reduce the energy needs to run the system and make it even more suitable for off-the-grid installations!

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Replies to This Discussion

Permalink Reply by Dan Ponton on April 17, 2012 at 9:44am

Just read your post. Have you done this yet?

How has it worked for you?I would be concerned about the weight of the raft being on the two ends only.

I saw a post from someone that built his rafts out of either PVC pipe or air filled sacks with plexiglass rafts, I think. The PVC held the raft above the water line an inch or so, allowing air under the rafts.

Permalink Reply by Averan on April 17, 2012 at 9:55am

Not yet...construction was stalled due to a few weeks of late season rain.

Good point about the structural integrity, although people pick up rafts of mature plants and carry them around all the time (by their two hands). Would be easy enough to add some additional support tabs or something similar.

Permalink Reply by Dan Ponton on April 17, 2012 at 3:20pm

Yup, I have seem that a lot of you-tube, but I think it's with the 2" foam rafts. I think keeping the raft a little above the water line is a good idea, but I am new at this myself.

I will use one of the two ideas myself.

Permalink Reply by Bart on August 28, 2012 at 7:10pm

Averan, did you ever build this system?

I'm in the process of building a hybrid system in my basement for winter and looking at raft designs. Did you go with the lip idea, and have space under the rafts? Pic's would be great if you had them, and any commentary on what is or isn't working out for you would be very much appreciated.

Cheers

Permalink Reply by Tray Rasco on September 9, 2013 at 11:12pm

I understand it is called Floating Raft system. However I have been thinking about a fixed height with maybe some 1/4inch plywood painted with a marine based paint or fish safe paint and backed with some 1x2 strips to prevent sagging. I would then use a standing drain pipe to control the height of my water much like you would in a pond. This would allow for plenty of air no foam touching water to create algae.