Backyard Aquaponics
A place to discuss aquaponics

I have 4 tanks. I figure that if I get enough fry I can just process the excess females into fish emulsion fertilizer for the dirt garden or blend them up and make feed out of them.

I may add another pond or enlarge the existing pond this next spring.

Looking at aeration I found some interesting info:

EFFICIENCY


This is the general idea of how it works:


Growfish [dot] com uses the same method(s) to aerate densely populated fish tanks. A 6 inch pipe is held at 8 to 12 psi; both water and air are injected. This produces more than enough oxygen for the fish without blowing massive amount of air. It would seem to be cheaper to install and run than blower systems. I can get a good pressure pump for $89 while a blower cost much more.

So.. That has got me to thinking how can I achieve this effective aeration with minimum investment. This is what I am thinking. I should aim for the low pressure of 8 or 10 psi. Fresh water produces .43 PSI/Ft so a 20' water column will have 8.6 psi at the bottom. If I use a water pump and a venturi air injector I can pump water to the bottom of a 20 foot column of water and hopefully achieve good DO by the time the water reaches the top.



Now, I dont want to have a water filled pipe sticking up 20 feet in the air nor do I want to bore a hole that deep. So I am thinking I will bore a shallow 10 foot hole in the ground. A ball valve might achieve the pressure in a shorter column of water if the venturi will function under pressure like like this.



Will a venturi function with both sides under pressure and suck in air at atmospheric pressure?

Keeping pressure is a fair cost in pumping use,,, just something to think about. That and simplicity is the reason I have chosen the "oxygenation cone" type,, extremely simple and easily placed anywhere in system ,, even easily mooved if needed.
What amazed me was a recent diagnosis of a failing aquaculture recycle system ,, the variation in O2 at various points within the system where HUGE,,, sometimes it is a trap to think o2 is ok at tank ,, but what about coming out of pre-filter , or out of beds etc. Fairly simple to plump in TWO "cones" to try and keep O2 levels more stable throughout the cycle.

Be interested to see what you come up with DDM. I have been thinking along more simple lines of a spiral wheel of piping driven by a simple motor and with outlet at the base of the pond to increase DO as well as flow-form waterfall from the top. Inexpensive.

Checked out the cones Chappo. Neat solution but pricey.

Dan, you could possibly make something like this to inject oxygen although it was made to inject and saturate compressed oxygen. The water comes in on the right side and a flowmeter and oxygen hose is attached above it. On the left is the outlet and pressure guage. About 20 PSI works well.

Also, about your overpopulation of Tilapia, maybe put an Oscar in each tank to eat the excess fry. Then you can eat the Oscar later.

I am not willing to buy oxygen(even at 2 cents an hour). Chappo, are you using oxygen with those cones or air?

I understand pumping pressure is costly, but its cheaper than buying and powering a rotary vein air pump and cheaper than buying oxygen and its simple too. The trade secret is what psi they run at to achieve the flash of micron sized oxygen bubbles to oxygenate the surrounding water, but even without that Im sure it works. Growfish only uses 8 to 12 psi..

Here is a video of the device, using pure oxygen..
http://www.youtube.com/watch?v=23S61iA4I2E

Dan definately just air , I am also unwilling to pay for pure oxygen , I think it's an unnecessary ongoing expense.

Cyra ,, expensive??? It's merely a cone with a pipe in , and pipe out, can't see it being more than $10 to build one.Maybe $20 for a good air INJECTOR.... First one i will make will need to be perspex or at least see-through so I can get the flow rate and injector air rate matched , after that can be made from anything.

JDPhish ..... what you show there is merely a u-tube ,, just built at ground level ..... looks cute.

Chappo, that's exactly what it is. Works too. I was just showing this as a possible alternative to a cone or 20 foot pipe. Seems you could just inject atmospheric air with a venturi and increase O2 saturation. I wasn't suggesting the added expense of pure oxygen.

I only suggested a 20 foot pipe as a low pressure alternative. I was also thinking that if I could bury the pipe in the ground I might gain some benefit from ground temperatures. The add-o-mizer uses a short piece of pipe. You can see from this picture that its barely taller than a fish tank when run under pressure.



From my understanding oxygen is absorbed into water faster as pressure increases from 8 to 50 psi. So, the length of tube needed is reduced as the pressure increases. I am may try to replicate this device.

I am still weighing out the cons & pros between the add-o-mizer and an open pipe and I had another thought. The problem with down flow devices and air is that most of the air is nitrogen which means you build up a large bubble in the top of your chamber until most of the water is displaced loosing your oxygen dissolving ability. Now, my well tank has a blow off device installed to remove sulfur smells which works via float and releases air out of the pressurized tank which is injected each time the pump starts. So why would this not work perfect for an oxygenator? Water and air(from venturi) would be pumped into the bottom of the tank, oxygenated water drawn off in the top to middle of the tank and the blow-off valve would release the excess nitrogen and unabsorbed oxygen(and other gases). This system would not have to be pressurized even. It would just be a place to maximize air and water contact time and release unabsorbed gas.

These tanks are rated for pressure and readily available with the blow-off valve already installed.

I could perhaps even drill a hole in the side and use a uniseal for pressures up to 40 psi..

I finally received my oxygen test kit. I tested the water in the pond before sunup and the DO was 3 to 4 . I tested again before the sun went down and the DO was 8 to 9.

Wow 3-4 thats pretty low

Well I forgot to take pictures of the salad and veggies with the fish, but we enjoyed another all AP meal last night

That brings us up to 39 AP meals this year (in the last 2 months).

The salad had some of that weed that is high in protein too! Whats it called?

I have always filleted fish before and have never gutted one, so I gave it a try and the result was a very tasty meal. I had a little trouble with the fish sticking to the grill..


Three fish was plenty of meat for a family of 4. Here are the uncooked weights:

That's the nature of the beast... DO will always be at it's lowest pond before sunup... and will usually max out late afternoon...

4-10 would be pretty typical for most AP systems.. IMO...

jdphish ,, I wasn;t suggesting you were talking pure oxygen , that was a reply to another question.

yes ,, a wall mounted u-tube ,, all the friction loses ( PLUS MANY EXTRA WITH THE BENDS)and minus most of the pressure advantages, .....,, thanks for the input.

Ok the add-o-mizer system operates at 35 - 40 PSI (207 kPa). This is enough pressure to super saturate the water so that oxygen bubble flash out of the water when added to the pond and oxygenate the rest of the water with micro sized bubbles.