Venturi aeration design

[Chelsea Brannan]

Hello Aquaponic Friends,

I was looking into adding a Venturi unit on my incoming water pipe that returns water from my DWC Trough to my Tote with the fish. I came across this great video from a trusted source that uses them in their fish hatcheries.

Does anyone have any experiences using these for added air? I am trying to avoid adding another electrical expense by running a large air pump. Any thoughts?

Here's the video:

https://www.youtube.com/watch?v=IZyrL5Ojqpo

[George]

Sure, try it.  The gravity fed return won't have nearly the pressure of pump fed but if it increases your aeration, why not?  Looks like a fun project.  You can use a stainless screw to hold, instead of silicone, if you prefer.  Good luck.

[Jim Troyer]

Chelsea:

Whenever you have a hole at an angle like that you will get a draft or suction from the fluid moving past the hole.  George is correct, there isn't much velocity to create a suction there.  My advice for what's worth; is if you have plenty of flow rate, is to create a tee off the main water pump line and send part of the water back into the fish tank with the venturi like the video has in that line, instead of the drain back tube. 

Another method of adding aeration is to create an "aeration tube" for your return water.  You can do this by adding a larger diameter tubing filled with some media to stir up the water flow.  Use a tee to create an air source above the aeration tube as well.

similar to this crude drawing:

[Chelsea Brannan]

thanks guys! I would be adding the venturi to the pipe that comes off my pump and fills the fish tote. Eventually that water drains into a swirl filter then my DWC trough. So I figure the fish will benefit most form this location. Right now I just have a spray bar that has too many hoes and does spray very forcefully (see pic below). I am fishless cycling right now so I want to get the aeration worked out before I add them.

[Jim Troyer]

Chelsea:

Depending upon how many fish and hours of pump cycling that spray bar should do the trick.

If you find the fish are sucking air, you know you can add the venturi later.  Your fish will be small this season and will have no problem with DO until next summer. FYI: Bubblers are just there to keep the water moving via the fiction between the air and water molecules, the actual bubbles don't add much aeration.

I always try to create a swirl in my fish tank to create a current and to keep things moving longer after the pump stops (on 15, off 45 minutes per hour).  So far in 118 degree heat (Saturday) it's enough in fact neither system seems to know how hot it really is (and it's freaking HOT!)  My in-ground pond has fry in it for the first time  .

I've been cold and hot , -40 in a blizzard and 122 in stagnant heat. It feels like basting the turkey out there right now.  Just stay inside when it hits an extreme like this.  Good thing it's only for 4-5 days

all the best!

[Chelsea Brannan]

hmmm, ok I was concerned that with a 225 gal tote, 55 gallon swirl filter and 16ftx4ftx10 in deep DWC I would need more oxegyn. I have no fish in there now but plan to add 100 yellow lake perch fingerlings later this month. I know the fish and plants wont mind the added oxygen so i thought why not try to Venturi.

[Jim Troyer]

Well Chelsea

1 fish per 2 gallons is going to be pretty tight...

You should have enough grow bed for that many fish so you may want to consider planning another tote in series to give the fish some elbow room.

Bubblers in the grow bed will help your plants grow more vigorously.  You will want to have an air gap between the water and the bottom of the raft.  I've seen where they put closed end PVC or pool noodles under the the rafts to keep a portion of the roots out of the water.  Another thing that is happening here in AZ, is a solid structure for the holding the net pots above the water, with the pots just touching the surface of the water.  Which works really well.

I started my addiction with a raft system.  I have now morphed it into a hybrid system with 2 liter soda bottles filled with volcanic cinders to hold the plants that sit in the DWC. tank.  I felt the roots got too tangled to do anything with the plants except harvest them.  I wanted to be able to move them and check below the raft, but it was such a mat of roots it was impossible.  I also didn't use thick enough foam.  The plants got so heavy they sank on 1" blue foam.  If you are interested in knowing more about the way I handled the 2 liter bottles I add some detail later.  Where do get enough bottles? Just ask your coworkers to bring some to work, the gal with a desk next to me brought in 4 large garbage bags the next day...

good luck Chelsea

BTW: what is your location?  Perch won't make it here in AZ...

[Chelsea Brannan]

I am adding another tote and 4x16 raft  to this current system. The fish will get separated between the two eventually. Who knows I may have the other one built before they get here. (The place that I am ordering them from said they should be pellet train for feeding within this month.)  I figured they are small enough now, if they happen to all go in one tote for a few weeks. I'm at the mercy of the hatchery for timing, lol! I am in Wisconsin, hence the use of Yellow Lake Perch. They are native to my state and can tolerate cooler water temps in the winter, even though I will be heating the hoop house. (And the only provider of Tilapia in my state is way over pricing their shipping and are too far away for me to drive over and pick the tilapia up...so Lake Perch it is!)

[Jim Troyer]

I though perch was an excellent choice actually, Friday night fish fry here I come!

Tilapia have a hard time handling our winters here in the Phoenix metro area.  My in-ground pond got to 48 degrees last winter.  For perspective, I went Ice Diving (scuba) as a kid, it was 55 degrees under the ice near my home town in SD, it was 51 degrees in the swimming pool when I got back here a week later.  The desert is a land of extreme temperature changes.  On a daily basis a 30- 35 degrees is an average temperature swing.  40f overnight and 75f at noon, gotta love the winters, a few weeks in summer is rough however.

[Tim Day]

Hi Chelsea. Water has a maximum saturation point for oxygen that decreases at higher temperatures. After a point, it doesn't matter how much bubbling you do, you won't be able to increase DO. If there isn't enough oxygen to go round in the tank you will have fish deaths.

So your fish stocking ratio is probably going to be pretty tight for DO no matter how much aerating you do. I would suggest either not putting so many fish in or increasing your fish tank volume. Could you reduce your fish order until you have more space set up?

The rule of thumb for stocking density is one fish per 5 - 10 gallons of water, and I lean towards the ten side because it gives you more time to react if you ever have a problem with your pump or a power outage.

Good luck!

[George]

Sounds like a good plan to me, Chelsea.  

Stocking Density–

• 1 pound of fish per 5 – 7 gallons of tank water (.5 kg per 20-26 liters)

[Chelsea Brannan]

I am cleaning out two totes tomorrow, and getting them ready to hook up to the current system. So I should have about 30 fish in each tote, when all is said and done. The hatchery only sells in groups of 100, but when they get here i'l have them split between the totes. I think I would still like a small venturi the surface water of each assuming the first one works well. I'll post pics when it's built and installed.

[Jim Troyer]

That should work out well Chelsea

I'll give you a perfect example why you need the extra wiggle room.

This morning, (7/3/2013) I went out to feed the fish (40 various sized 4"-14") in my 700 gallon jacuzzi system.  It is hidden around the corner and the fish are very shy compared to the in-ground pond by the patio. I thought there were a couple of fish sucking air when I first got there but they turned and hid in the depths.  So I sat down in the chair to observe for a few minutes.  After they had all eaten a few fish would surface to suck air for a few seconds.   I also noticed the water was darker than normal as I can usually see the fish in the bottom, not today however.  The pump was not running but that is normal on a timed system so I didn't think anything about it.

The day before I had noticed one or two of the little guys were sipping the top but none of the bigger fish, so I chalked it up to being 118 degrees and reduced DO capability of the water.  On the way back inside I added an extra 15 minutes to each cycle so the pump would run 1/2 hour of every 2 hr cycle.

So this morning with more fish having trouble, I decided to turn on the pump manually and run it for a little while extra. I flipped the switch and walked around to where the system is and the water wasn't pouring out of the GB feed pipe.  I checked the pump and it was too hot to touch.  I unplugged the pump and after it cooled a few minutes, I took it out and went to the work bench to remove the pump cover so I could check the impeller.  There was a single piece of hydroton stuck between the impeller and the housing!  I fixed the pump, reinstalled it and everything works fine again.

3 days prior, I had a guy come over to buy fish and he brought along a 5 gal bucket of hydroton to soak in my system to get a quicker start cycling his system.  Not being a hydroton user I was unaware the clay balls would float.  I put his bucket in one of three interconnected 32 gallon trash cans I use for sump tanks and some hydroton floated but I figured if it floats there would be no problem.  Well it turns out, hydroton sinks after a while... A few clay balls ended up going through the pump and into the grow bed and several others had made it through 3 sump tanks but only one got stuck in the pump before the cycle of chaos began.

I don't use air stones or anything else in either my systems; I rely on the splash and circular water flows for DO and now I know my system has enough DO buffer so the pump can be off for 2 or 3 days without killing my fish or the plants. 

I'm very pleased that I have built into my system a large enough margin of safety that I could be so absent minded to not notice pump failure immediately and not kill everything in the process in a maximum hot spell of 118 degrees in the desert sun.   

I'm still wondering why everybody worries about additional aeration, air stones, back up power supplies, solar and what not in case the power goes out for a few hours...  Over crowding is a real issue, not DO, IMHO