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Aside from keeping the DO optimal for fish and plants, has anyone placed direct aeration under the physical plants and compared growth with those without? In a little experiment, I noticed a visible, positive difference in growth speed. Would agitation be a factor, stimulating the roots?

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In DWC or raft beds, aeration under the plants is usually beneficial.
I would think the DO would be highly beneficial, but also the constant agitation of the bubble column probably keeps more nutrients flowing through the roots.
Kobus, What's a good way to do this in a DWC situation? I have a few ideas that quickly come to mind but thought I would ask Master Yodaponics first. :D I am trying to get away from using styrenes if at all possible, without breaking the bank. My current DWC system is 8' x 32' of which I am planning on having 2 of these set up. Thoughts?

Once you put your rafts such that you have an air interface with your pots (do not place raft on water as a float, but on a lip of the raft bed) then you have 20 mg/L (ppm) directly at the root zone, which in theory is better than what you can do with aeration using air and not pure oxygen. >>
Some people use boards resting on the edges of the bed or on floats rather than the foam floating directly on the water. This could be heavy but would avoid the styrenes. I'm going to tinker with some different ideas for "rafts" that maintain a water/air interface as much as possible.
Here is an example of what I'm talking about. The growth is directly over an airstone.

I get what you're saying about raising up the plants for air to flow in between the raft-like container and the water. It would be simple to rig something like this up; however,will this damage the root base or dry it out?


This is an example of what I see over the airstones on a regular basis. (You should see the dramatic difference after only 2-3 weeks)
WOW that is an obvious visual!
Wait a few weeks, I'll do another picture. It's the reason I brought this up. If what he's saying is I can get results like that over the entire system just by raising the raft a tiny bit, that's dramatically going to improve.

TCLynx said:
WOW that is an obvious visual!
I'm testing out options for suspending the plant roots down into the water without blocking the surface from air.
However, keep in mind that the bottoms of your rafts are probably currently providing some bio-filtration surface area so if your system is designed without a separate bio-filter and the raft surfaces are calculated in to support your fish load, you might need to provide some added bio-filtration to take up the slack when you make the change.


Cory Torrella said:
Wait a few weeks, I'll do another picture. It's the reason I brought this up. If what he's saying is I can get results like that over the entire system just by raising the raft a tiny bit, that's dramatically going to improve.

TCLynx said:
WOW that is an obvious visual!
That's kind of how I have my current system set up Kobus. I have reused pudding cups filled with gravel as my pots. They have holes on the bottom only, as only 1/4" sticks down below the foam into the water. So generally I get about 1/2" of water in the bottom of the pots, and the rest is moist gravel except the top where it's dry. Seedlings have grown well providing the roots are touching moist gravel. Aeration is vigorous and about half of the cups actually have bubbles entering them. Those seem to have grown the fastest too. I have nothing to compare with so I have no idea if it's better than any other method.

I harvested a few lettuce today and most of the roots that were in the pot stayed in the bottom of the cup where the water was. Roots weren't very plentiful in the part of the cup that was only moist. Most of the roots were out of the pot in the tank. I should have taken pictures.

I can't wait to hear about your results!
It may also clean the roots. I notice many roots get a coating so they do not get as much oxygen / nutrients. Having the extra flow from the pump may be why they are doing better. Just a thought.
Does anyone know how to calculate how big of an air pump aperson needs to handle an aquaponic setup Troughs, tanks etc. Thanks .Paul
I don't know the rules about air volume (size/number/placement of stones) for raft beds.

However, one rule I have been told for air stone aeration of fish tanks is that you would want 1 cubic foot per minute of air for each 400 gallons of fish tank and that you need 1 psi to push the air though the air stone and 1 psi for each 28 inches of water depth. You would want to choose an air stone appropriate for the amount of air you want to pass through it. (The aquatic Eco Systems catalog has this info for their air stones.) Anyway, so for my 300 gallon fish tank that is only 25 inches deep I would want an air pump that would provide at least 0.75 cfm at about 2 psi.

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