Backyard Aquaponics
A place to discuss aquaponics

Hi all,

for those of you who have seen my build, you will probably have a little laugh at me here.. I whacked in a few air stones on some good length of hose only to find that the pump is not capable of pushing air down to the bottom of my FT...(6'9") all air flow stops about 2' from the bottom. I was thinking of using my return from sump to inject air right down low, like the venturi type setup...

thoughts, ideas... etc welcomed.

trout turning up soon so i want max air/oxygen injection.

cheers

Hmmm, you'll find the venturi will start to struggle as well I think Steve. Having the air 2 feet from the bottom isn't too much of a problem, the rising air will cause water movement so things will mix well. Plus 5 feet of air bubbles rising is a fair bit....

Only other answer is a bigger air pump I guess...

Simple drop a 90 mm pipe right to the bottom of the ft with a few 1/2 holes right at the bottom and put a tee to exit 6 in under the water level drop your air stones 1/2 way down and turn on [kind of like an airlift pump theres a few running around the traps no problem

Yah - as they've all said, it's the water movement you want - getting the O2 deprived stuff from the bottom and up and mixing with the O2 rich stuff at the top is good enough.

Simply putting one of the air stones in PVC that reaches down near the bottom of the tank will create circulation and will cause stale water at the bottom to come up to the airstone.

I have used the return from my BS to push the introduced air in top of the bell to go to the bottom of my IBC, runs for about 4 mins (250 litres). Keeps the crap off the bottom too. Pushes down between 700 - 900 mm.

Hi all,
I use a home made venturi :

attached to a 25mm diameter By-Pass line from the main Fish Tank submersible Pump for 24/7 aeration at about 800mm deep discharge.

I also have an automatic 12V/240V relay switch attached to a (continuous top-up) charged, 12V battery operated, Bilge pump with a Power Stream Venturi for 240V power outages to keep high DO in the Fish Tank when the main pump is not running.

This is in addition to the gravity flow return water (in a 90mm diameter PVC back vented stack pipe, fed by the Auto siphons) from the Grow Beds and a 25mm diameter Fingerling tank return pipe which have sub-surface and surface splashing actions respectively etc. but only when the main FT pump is operating.

From research and anecdotally, the deeper the introduction of the air stream, the greater the level of Oxygen dissolution because of the differential pressures. It is easier to push "water bourne" air in a Venturi arrangement to depths not able to be achieved by air pressure alone (i.e. Air pumps/Compressors to air stones and the like distribution systems.) I also think that the introduction of seperate air supply pumps/compressors, lines, stones/diffusers and the like introduces another level of power consumption, more areas for equipment to fail and still does not cover the event of back-up for power failures. Plants can survive a lot longer without water in the Grow Beds than Fish can survive without oxygen on the Fish tank.

For your information only, I'm not pushing any barrows!
Cheers ianK

Thinking of running a pressure pump back to FT from sump with venturi. return pipe into tank around 25mm with bleed holes for air/ water distribution starting 1.2m below surface. found a few pond/dam air pumps with greater pressure range... but at a greater price and wattage too.... after its all sorted i will put in an inverter 12vdc -> 240ac so i can keep plenty of air available in worst case scenarios.

cheers people.
Steve

ps: trout here in 3 days!!!!!

Hi Ian, Read your complete post this morning, good to hear that you are back on your feet again.

For those trying to figure out what air pumps can do for you.
Plan on 1 psi being used to push the air through the air stones.
Then plan on 1 psi for every 28" of water depth.

So if you have a 6' 9" deep fish tank, you need 2.9 psi just to push air down to the bottom and another psi to actually push the air though the air stone. An air pump that can give you a good amount of air flow (like 2 CFM, ok I'm assuming about the size of the fish tank but I was guessing some where in the range of 800 gallons) at 4 psi is probably gonna be kinda rare.

I've got an air pump that gives me 2 cfm at 2 psi and it is working well for my system where the water depths are less than 4 feet. It uses less than 60 watts and is supporting 4 tanks and is also my battery backup.

Wouldn't returning your water from the growth beds to the bottom of the tank stir up the water enough for aeration. Add one of the air lift tubes mentioned above and you should have plenty of air. Is that right??