Backyard Aquaponics
A place to discuss aquaponics

I can't find the answer to this question. Some research indicated that air added into the FT disrupts the flow, and should be avoided. So do I just add air in my filters and degassing tanks. Initially, I'm not planning on having any hydroponic beds, just a 4000 gallon RAS, so fish health is my primary(only) concern.

"Some research indicated that air added into the FT disrupts the flow" is that because the aerated water is being sucked into the pump or SLO?

I thought the air bubbles themselves did little to the DO but rather it was at the water surface where the increased surface area increased the oxygen adsorption?

So I would put it in the FT somewhere above the outlet level where maximum surface agitation was generated.

SB, The disruption is from agitation of the current that the discharge pipes create. I plan on having my piping go the height of the FT, with nozzles angled to create the best circulation throughout the water column. I just want to plan the thing out the best way, and not make mistakes at this point. I can't find any info on the best place to aerate the water is. Found rates for DO, rates for air volume per FT size/fish density, rates for DC beds, but can't find where to best utilize air for fish. There has to someone out there who knows this one.

I have round tanks and suspend the airstones in the centre. That way it doesn't affect the circular flow but at the same time draws water up, across and down the sides, helping move solids towards the slo.

Coachchris,if you employ an open inlet into the fish tank,then add a column of air in the center of the tank you will have two directions of flow,first will be the surface flow caused by the inlet,second will be by the air column in the centre of the tank which will have the effect of dragging water down the sides of the tank across to the centre column or your bottom drain. If you are going to utilise a Cornell type manifold that moves the entire column then you need to oxygenate outside of the tank.your degassing chamber is a perfect example of this.

Thats what I was trying to say !

Rendang,apart from the fact that if you use a inlet manifold that moves the entire column of water adding air will disturb the flow to the centre of the tank,in this case external aeration is better and more suited.

Rendang, thanks. I'm thinking a center drain/Cornell type set-up. But am thinking how hard it's going to be to ensure the drains don't leak when they're buried. 2 of my FT are taller then wide, and will require digging in. I will have equipment to dig the holes, but still wonder how I'm going to know if they are leaking or not. i will employ bulkheads, and hope for the best. DB, thanks...that what I was hoping for...a location. Do you have a reference to size and retention for the degassing tanks? I will have back airstones in FT's, but only for power outages.

Why would it be a bad idea or at least not the best to place an air stone in the center of a Cornell style tank?

Wouldn't the air stone enhance rather than disrupt the currents you are trying to generate with one of these tanks?

Stuart from my understanding on Cornell Culture tanks,the flow through the bottom drain is as little as 5% of the turnover,the rest goes out through the side drain,with the tank turning over between once and twice per hour.The design of there inlet manifold moves the entire water column which sweeps the bottom moving the solids towards the bottom drain,the circular flow in these tanks creates in its own right a secondary radial flow which also assists in the removal of solids to the bottom drain.
There is absolutely no reason why you can’t add an air stone to the centre of these tanks,but its not required as the design of the tank makes it self cleaning,with the disruption caused in the centre of the tank around the bottom drain would this be hindered ? and in shallow tanks how much benefit would be derived from this ?
I followed cornells example when i did the layout of my tanks,bottom drain and surface drain only i split the flow through both,bottom drain to the swirl then media beds,the surface drains through there filter and on to the DWCs,i have recently switched over to timed flood and drain,30 on,30 off and because of the interest you sparked off concerning air lifts i am trying a very simple 3/4 airlift attached to the manifold and facing in the direction of flow so as when the pump switches off i still have movement and aeration.With water temps of 30c during the hot season keeping o2 levels up is a problem.
The UVI placed there air stones around the outside of there tanks i believe.

Yep, spot on.


Yes again.



Know idea It is conceivable that a greater circulation rate caused by the updraft current of the air stone could cause a significant decrease in the efficiency of the bottom drain removing solid wastes.


Again no idea but what do you mean by shallow? What sort of ratio of depth to width?


Hmmm. Sounds good we await results. Now that you mention it they did have them round the outside. I would have thoought that this would have disrupted self cleaning current because around the outside of the tank it would be going down the air bubbles coming up would certainly disrupt this. Maybe it doesn't make much of a difference?

Forgive me for not reading this entire thread but...

I have an IBC FT with 1.5" return line feeding it. Currently I have a spreader bar which consists of nothing more than a length of PVC with a bunch of holes drilled along one side. The water sprays out of the pipe and disrupts the surface along one half of the IBC.

What if I removed the spreader bar and replace it with a T-connector placed vertically... left the top side open and placed a length of PVC reaching nearly to the floor of the FT. Near the bottom but inside the vertical pipe I placed an air stone thus forcing the air to bubble up through the filling water column... would this increase DO in my system more than the current spreader bar?

Yes i feel it would as the contact time between bubbles and the flow of water gives you the best scenario,commercial oxygenators work in a similar fashion,but how much of an improvement over your current system is hard to tell.

I was looking for pictures to back up my post on oxygenators and found this,coachchris this should be helpful for you.
http://ag.arizona.edu/azaqua/ista/ISTA7 ... nation.pdf

Have I missed something here, are we talking about air or O2 injection?