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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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Hi Chris,Frank,

I like your point Chris and we certainly cannot discount the fact that air bubbles accumulate at the root site. A good analogy to use here would probably be Aeroponics, where large amounts of air and moisture are introduced, resulting in phenomenal plant growth. While i have not seen any comparative data on agitation vs aeration in trough culture, at the same time, bubbles are causing agitation to the surface water under the foam mixing air/water while increasing DO levels(especially if we use larger bubbles) in a trough that would otherwise depleted of O2 by plants sitting in calm slow moving water in long runs.

And Frank's point(if i understand correctly), these tiny bubbles in our troughs do not greatly impact DO levels which are ultimately important for mineralization and fish growth etc. As in the case of commercial raft they can avoid this in some part by the process of solids removal in their systems.

while smaller bubbles expose exponentially more surface

diffusers and other systems that produce small bubbles tend to clog much faster

so they need much more attention

and when under the floating rafts they are barely accessible

fast solids removal from the fish tank is as essential as oxygenation as the two go hand in hand

Frank

The air-stones under my rafts are very easy to access and have not clogged(as of yet). I use a fine pore stones. Some stones have been in service for nearly two years with no cleaning. A raft system that is rotating crops will have rafts removed for harvesting/replanting on a regular basis.  At that time is is very simple to check the status if each stone. Each stone in my troughs has its own valve so I can ajust each one and get an even distrobution down the trough.

 

This video made me reconsider my idea of the optimum air requirement for my raft bed. After watching this I went out and got a bigger air pump(GH Dual Diaphragm 8watt, 20 LPM or 320GPH, 3 P.S.I.) and put 4 airstones under my 4'x16'x9" raft bed. I probably don't have enough airstones. I probably could use a second line of 4 stones but dont want to spend more now.

http://www.youtube.com/user/SureToGrowers#p/u/11/ckAKVljIB2U

Conrad

Hi All,

In my small raft i compared grow out time with and without added aeration. From visual observation I estimate between a 20-30% increase in plant size over the same period( this is not weight of plant) using air. By increasing the pore size of the stones i see a sightly better conversion time for nitrification. Do you have the same results?

Without doubting your honesty, Chris, I find that hard to believe

visually checking the status of each stone can be very deceptive

having a separate valve is a good thing but influences the observation:

when a stone delivers less air, one tends to just open the valve a little further

but undoubtably the bubble dimensions will change and so will the volume

you may be under the impression that nothing has changed

it is very difficult to explain but bear with me:

an air pump relies on pressure to force the air below water level

so by definition you have to keep the pressure up which means you can never release the surplus pressure nor the surplus volume

you have an air pump with a manifold from which tubes lead to your diffusers

There is no way you can leave one end of this manifold open, because then no air willflow to the diffusers

so by definition you have to strangle your air pump

that is one of the differences with a water pump:

The purpose of a water pump is volume, not pressure

but  you can have a water pump with a manifold with one open side that allows the surplus water to freely flow back to the fish tank

Frank

The valves on my air stones are out of necessity. M air pump supplies my fish tank and my troughs. My fish tank is 42" deep and my troughs are 12". Without valves on my air-stones all the air would would blow out in the troughs. It is much easier for the air to exit through shallower water. I valve the troughs not the FT. The depth of my FT sets the pressure in the air system but is allowed to leave.

what I meant is that due to the compressability of air (a gas) your compressor or blower or air pump is necessarily strangled.

So quite a big part of the energy is transformed into noise, wear and heat

in a good design there is no necessity to strangle a water pump: just pump the water straight up to the necessary height, using a wide tube on the pump exit then let it free flow to wherever you need, preferably in open (but shaded) gutters with turbulent flow (just put some stones or other in the gutters to make the water swirl).

You can then put valves (metering and/or controlled on/off valves) on all exits except one (preferably the one going back to the fish tank): your pump will always give it's maximum volume for the energy input.

the surplus water will go freely back to the fish tank,

we agreed that volume is what we need:

for fast evacuation of solids and bacteria out of the fish tank to the biofilter, for maximum nitrification and for maximum aeration

surface exposure and oxygen exchange will be optimal

Frank

So Frank, I can agree that for aerating a fish tank, water flow can be designed to be enough.

 

However, with only 5 gpm of water flow through a raft bed and a long run under rafts How do you make the water flow provide all the needed aeration for the rafts down their entire length (which can often be hundreds of feet since raft beds are often chained together.)

I need to do some calculations, then I will reveal my solution
Frank
TCLynx said:

So Frank, I can agree that for aerating a fish tank, water flow can be designed to be enough.

 

However, with only 5 gpm of water flow through a raft bed and a long run under rafts How do you make the water flow provide all the needed aeration for the rafts down their entire length (which can often be hundreds of feet since raft beds are often chained together.)

This is getting exciting!

I will admit I have not read the whole post of comments.  Aeration under hydroponic plants has been well documented... for decades.  I had to prove this point the other day at work, and pulled out a plant textbook from the 70s with clear pictures just as you have shown.  I bet the roots were way more developed too.

I personally think it has to do with the oxygen content of the air being higher than in water.  Most of us in aquaponics get away with the levels we do because of flow and drain media beds, or nft and towers having low flow high air space, of the vigorous aeration needed to keep the fish alive.

The key for your raft system is to not over do it.  You don't want the aeration to come up through the pots, leading to your plants sitting in a puddle.  Anything below this should help out greatly.

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