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Dr Wilson Lennard is a recognized authority on Aquaponics. Here he is speaking on Aquaponics as an Ecosystem. This clip was from Murray Hallam's Practical Aquaponics Blog

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Comment by Kobus Jooste on February 6, 2011 at 10:31pm
If I ever get to complete my commercial system that I would like to build, I will go for raised beds with cascades, but more importantly an add-o-mizer pressure vessel.  It will easily get you to saturation point and above (becuase it is pressurized, it operates at a different "atmosphere" pressure, and as such, the oxygen partial pressure is higher and the water absorbs more oxygen).  Oxygen escapes very slowly when the water is returned to normal pressure, thus the advantage is still there when the water is pumped into a raft.  You can work with atmospheric air, thus do not need to go for pure oxygen or ozone.  This is a relatively small piece of equipment - kind of like a large canister filter body, thus will not be difficult to add in somewhere after the main pump and before the raft.  Just don't know what one of them costs
Comment by Michelle Silva on February 6, 2011 at 9:32pm

and no the soaker tube would have been in the raft tanks, would not be agitating surface, which I am aware that seems to be the best method

 

Comment by Michelle Silva on February 6, 2011 at 9:31pm
I am interested in getting in as much oxygen as possible, would love for it to be as close to full saturation if it's simple enough to do, to increase plant growth rate even more. When Gina and Tanya were here, they reported that someone who had much higher DO was having phenomenal growth and I wouldn't say my growth rate has been phenomenal, just so so. As this is a small commercial system, I would like it to produce as fast and healthy as possible.  The fish seem to have plenty of oxygen. I think growth rates slowed down mostly due to the cold weather and very cold temp of water causing fish to stop eating, but I'm taking more precautions in that area now.
Comment by Izzy on February 6, 2011 at 8:23pm
Well, as our debate revealed not very much oxygen gets into the water from bubbles in the water.  However, if you are planning to use the tube to agitate the surface of the water, then it will definitely help add oxygen and exchange other gasses.  Can I ask, but why do you feel you need to add more DO to your water?  Do the fish seem to have enough oxygen?  Are the growth rates about where you expect them based on the food input?  If yes to the last 2 questions, you may not need to make the addition, but of course it's always fun to tinker!
Comment by Michelle Silva on February 6, 2011 at 4:13pm

Thank you both for your responses. I don't know if you saw pics of my system, but I would consider it a hybrid system. I have three raft tanks 40' long and 55 vertical towers (38 plants per tower in coco coir/slate and other mixed media)..The fish tanks now have spray bars on them as opposed to the previous set up where I had waterfall (where each cascaded into the next) and the rafts have just splash at the beginning and then overflow to middle raft tank at the other end. Three times a day the towers get watered and the water flows back after going through towers. I'm pretty happy that everything is doing well so far but I can only imagine if adding more splashing, and possibly more cycyling through towers and a flood and drain (to enter halfway down raft) that it will significantly add oxygen. I can't wait to get that set up. I think only after seeing what happens with that, then will possibly try adding soaker hose.  I'm not sure about justifying buying an add-o-mizer at this point.

@ Izzy-not same as a plain garden hose, it's usually a black hose with I think lots of tiny holes..would create lots of tiny bubbles. I wouldn't be pumping air into it, pumping water. I am not interested in buying an air pump for multiple reasons.

Comment by Kobus Jooste on February 6, 2011 at 2:09pm

Michelle - I am not going to suggest that you will see rapid increase in DO based on what you have described, simply because I have no idea of the velocity of water flow through, or extent of the soaker hose you refer to.  I have dedicated my efforts towards media and hybrid systems, thus people such as the Friendly Aquaponics people and Green Acres better understand their type of set-up and the conditions under which it operates.  I have been able to take my small system to above saturation level with cascades alone, while the large unit runs even without cascades - just surface agitation at three points in the fish tank.  It is very lightly stocked at the moment though.  The reason I am trying to work with cascades is, as you stated, the added running cost expense of air pumps.  I do not have extensive rafts, but if I did, I would take a large amount of interest in an add-o-mizer.  It is a once-off cost (not sure how much), not a monthly electricity increase.  It pressurizes a water and air mix, fluxes the nitrogen and thereby increasing the amount of oxygen that enters the water (by increasing the partial pressure of oxygen in the vessel).  The add-o-mizer is installed in line, thus I do not think that you have to get any extra pumps for it.

 

In terms of your soaker hose idea, I think the only way to determine if it is going to make a difference is to try. It will have to be set up in such a way that it does disturb the surface of the water - kind of in the same way as a spray bar would operate.  I think having it deep in a tank will dilute its effectiveness somewhat.

Comment by Izzy on February 6, 2011 at 1:31pm
Umm, it depends.  I'm not familiar with a soaker hose.  Is that just a plain garden hose?  Would you be pumping air into it with many holes punctured throughout the hose?
Comment by Michelle Silva on February 6, 2011 at 12:28pm

yes, interesting commentary..as I had been given the advise via a telephone conversation, when I was first building my system, by someone who claimed to be an aquaponics expert/ consultant...that "air stones or anything that doesn't break surface tension won't add oxygen". I wanted to try to it without lots of air stones to avoid the extra expense of an air pump, so was at the time kind of glad to hear that. I went with gravity splashing and figured I could add air stones after if needed. The gals from Green Acres Organics came last week with their DO meter and think it ranged from 65-80% saturation depending on where we measured..(Gina/Tonya, correct me if I'm wrong)..it was less in the IBC tote that had all the large tilapia and more in the raft tanks w/ the veggies..regardless, working on adding more splashing intakes to increase DO.

How much oxygen would you think adding a soaker hose under water would add? It would be easy and inexpensive.

Thanks for both caring enough to continue clarifying your points.

Comment by Izzy on February 6, 2011 at 10:44am

Again, you are missing the point entirely, and it baffles me that you cannot comprehend that Dr. Lennard stated diffusion does not occur below the surface whereas you and I both agree that it does.  Once you come to terms with that you might understand the moral imperative that an authority on a subject with a post-graduate degree should be more responsible with what he teaches to others, especially when he knows better.  With all that in mind, I feel it is wrong to disseminate erroneous information that others often take as gospel because the implications of building knowledge on incorrect information only leads to failure. Let's build our knowledge of aquaponics upon rock rather than sand.

 

"Therefore everyone who hears these words of mine and puts them into practice is like a wise man who built his house on the rock." Matthew 7:24

 

Have a blessed day. 

Comment by Kobus Jooste on February 6, 2011 at 6:54am
Any time :) !!

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