Backyard Aquaponics
A place to discuss aquaponics

Hey guys,

Any tips for providing fish their air? I'm aiming to use little electricity.

What about aquatic plants?

Probably a bad idea to use aquatic plant in AP. They steal the nutrients from the veggies you are trying to grow.

and they only oxygenate during daylight hours - at night they are consumers of oxygen

Plants photosynthesis during the day (using the sun), taking up carbon dioxide then turning it into oxygen. During the night, plants cant photosynthesis because there is no sun. They therefore use oxygen instead of carbon dioxide. Causing oxygen reserves to be depleted and the fish to be very sad

I use a 4 watt pump in my 1000 litre tank. To maximize its efficiency, the air stones are only 150 mm deep. I have placed the air stones inside a 50 mm pipe, which is approx 50 mm below the surface and approx 100 mm above the bottom of the tank. Overall length of pipe is approx 800 mm. This way, the air pushes the water up the pipe, from the bottom. It creates a current and aerates the water as it is pulled up the pipe.

If you place the air stones on the bottom of the tank, the water pressure will work against the air pressure and little air will come out. So you then need to use a much larger air pump, which will consume more energy.

Aeration primarily happens at the water surface. By disturbing the surface of the water the ripples make the actual surface area much larger. If you want to increase the aeration cheaply design your system to have the most surface area you can in the FT and let the returning water disturb the surface. This is why most fish aquariums are wide and short not tall and slender.

http://www.youtube.com/watch?v=X46_sHif ... re=related

Venturi effect for the win, man! You need to circulate the water anyway, why not throw some air in the mix as well? Beats the hell out of air stones/pumps!

I use a second cheap pump on a timer, the nozzle is about 10cm under the water surface. It seems to generate enough 'bubbles' to aerate the water in my tank.

It seems to be widely accepted that aeration primarily happens at the water surface.

However, I was uncomfortable with that and searched for scientific proof that actually proved
it either way.

Thankfully, a member on another forum posted this research:

http://digitalcommons.unl.edu/cgi/viewc ... myresearch



Just something else for you to think about.

cheers Lou

Yeah I guess if you pump "Oxygen stripping" nitrogen through the water it wont have much Oxygen in it. Then you use a mathematical formulation off of that data to come to results. That's U.S. Army corp of engineers logic for you. Hell we all know what a great job they did here in the everglades.

You can't change the laws of physics. The surface area of those bubbles is in no way even close to the surface area of the top of the tank. Oxygenation happens at the surface area, period. Whether that is the surface area of the bubble or the top of the tank. Unless there are little magic elven farie people in the bubbles that are granting Oxygen wishes to the fishes it ain't happening.

Anyway that's just how I see it. I could be wrong. After all I'm not a U.S. Army engineer. It's good to see someone use a "little" science and research. Either way neither is bad and either will work. I use both, You can't have too much Oxygen.

You understand that the oxygen was stripped out before they added any bubbles, right?

And that the nitrogen was used to produce bubbles that would disturb the surface and cause aeration but not add any oxygen of their own on their way to the surface? And that this test was done using procedures already accepted by the American Society of Civil Engineers (environmental engineers)?

Hi Patrick

Here is another experiment.






In this experiment they had the diffuser at a depth at 0.5m
and got 18-34 grO2/m3water.hr.

As soon as they lowered the diffuser to 4.6 metre the Conc O2
went to 160 grO2/m3water.hr ( a 470% increase)

If Oxygenation happens only at the surface area, how do you explain the
470% increase?

By the way this experiment was not done by the army, it was actually done in Iraq



cheers Lou

Very interesting. Will look over the link and reply...If you care to continue the discussion.
LOL did notice this in my quick look at the report and suspect it may color the results.

These parameters determine factors such as bubble
size and the degree of turbulence. Conditions in the
mixed liquor also have an impact on the transfer;

LOL Just saying.

OK I guess I should reword my response to the OP. In oxygen tansfer there are two elements involved. The water and the Oxygen suspended in air. Where these two elements meet is called the surface. If you can hook up an air compressor and crank it up to about 180 PSI, connect it to about 30 airstones you will be able to generate enough surface area on the bubbles to equal or exceed the oxygenation that happens naturally at the top of the water. Another option is to compress the oxygen by submerging the airstones to a depth of about 12 feet. Of course at this depth you will need a much larger air compressor.

So in closing if you have unlimited funds, a tank that is over 12 feet deep or some Iraqi scientists you can accomplish this. Of course you were asking how to do it without any of this so I guess you should just ignore me.

Standard Airstone running at 3L/min

Bubble size 2mm
Terminal velocity of bubble .15m/s (Taken from Perry's Chemical Engineers' Handbook Chapter 6 Fluid and particle Dynamics fig 6-59)
Depth of tank 1m
Transit time 6.7s
Volume of air in tank at once air stone has been running for more than 10s 0.33L
Volume of a bubble 4.1888E-09m3
No. of bubbles 79,577
Surface area of a bubble 1.2566E-5m2
Total surface area of bubble 1m2 per

Ceramic Air Diffuser
Bubble size 1mm
Terminal velocity of bubble .1m/s (Taken from Perry's Chemical Engineers' Handbook Chapter 6 Fluid and particle Dynamics fig 6-59)
Depth of tank 1m
Transit time 10s
Volume of air in tank at once air stone has been running for more than 10s 0.5L
Volume of a bubble 5.236E-10m3
No. of bubbles 954,927
Surface area of a bubble 3.1416E-6m2
Total surface area of bubble 3m2 per

If you use a proper micro bubble air diffuser with a bubble size of .5mm.

Bubble size 0.5mm
Terminal velocity of bubble .05m/s (Taken from Perry's Chemical Engineers' Handbook Chapter 6 Fluid and particle Dynamics fig 6-59)
Depth of tank 1m
Transit time 20s
Volume of air in tank at once air stone has been running for more than 10s 1L
Volume of a bubble 6.545E-11m3
No. of bubbles 15,278,838
Surface area of a bubble 7.854E-7m2
Total surface area of bubble 12m2