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How to Build a DIY Heavy-Duty Venturi for Direct Aeration of Pond Water


For great fish-keeping communities visit my favourite forums at:-

They are very friendly and knowledgeable groups of people who will make you feel very welcome. There is tons of discussion going on about fish of all kinds, problems whether relating to the health of your fish or the state of your pond, and advice on filters, pumps and anything else you can think of!

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A lazy summer afternoon in Nature 3D Screensaver

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During my search for information on how to build a DIY venturi I got in contact with a guy called ZikZ@k (Mark H) who frequents the American Water Gardening Society (AWGS) Forums, and who has kindly given permission for me to include his ideas on venturi design, that include an intrigueing "toothed" design. This page is entirely Zik's own work, combined with information from our email discussion on the subject.

Whereas my "Bio-Filter and Venturi" project required a light-duty venturi capable of operating with a low-pressure water pump into a Skippy style bio-filter, Zik's designs are for the more conventional purpose of aerating the water directly in the main pond, and therefore can be driven by larger pumps, producing more intense oxygenation of the water and giving current for the fish to swim against, and better circulation of water in the pond.

Zik has prepared a PDF document which this page is based upon that can be downloaded by clicking here. Also read the Additional Hints & Tips section for extra details and pics not included in the PDF.

Thanks Zik for all your help!


This page covers the following topics (click to jump to them):-

Over to Zik.....

Basic Venturi Construction for the DIY Crowd

"I have been thinking about this for a while, doing a small write up and trying to explain different construction
techniques for a common venturi using fairly easy to find materials. The materials that I have used here have been found at several places. A good hardware store / home improvement center and the aquarium store is all it amounts to.

The tools you will need are of common variety. Pretty much general tools such as a razor knife, an xacto knife, a
triangle file, a drill, etc…

Do be careful with any sharp instrument, tool, or power device. As with all DIY projects, it is possible to hurt yourself.

I am only showing three designs in this document. I have made many venturis for many different projects. You do not necessarily need to use the materials that I have depicted in this file. My material list changes continually to meet what I have on hand, as well as what I am trying to accomplish. Using this same basic design I have made venturis up to 2”.

This file is meant to be public domain. You can use it how you see fit. Copy it, pass it around, I don’t care. If you hurt yourself, I didn’t do it. If you eat the venturi after you make it, the hospital bill for removal is yours. All responsibility for anyone reading/using this file lies with the person reading/using this file.

Now, with that out of the way… Some kudos are necessary!

Gene Winstead, the owner of Koi Village gets a plug here. He has been a friend since shortly after my wife and I got into keeping koi. His help has been appreciated by both of us.

Kudos go out to Greg Bickal and John Johns for their contributions to the DIY crowd.

People that post anywhere, sharing their knowledge with the rest of us, you deserve a plug here too! Special thanks to the members of the Water Gardening Magazine Forum, and the KoiVet Forum.

On to the Goodies….

1) This inline ½” venturi goes to a submerged media filter. It has an adjustable air intake to make it work properly above water level.

2) Wider field of view from above to show the air intake.

You will notice that I use a wide variety of tubing to reduce the air intake size on almost all of the venturis that I make. It is good to have several sizes of tubing on hand for a lot of reasons, this is one!

A side benefit to using pressure fit parts is that it makes the tip adjustable. This is handy for adjusting the venturi to your pump, depth you wish to use it at, and amount of aeration desired.

Keep in mind that the materials used here are not necessarily the materials you will use. This same principal and these two designs are meant to be used for demonstration purposes.

3) 1” venturi with silicone air tubing and an air stone as an air filter. The body is a nylon 1” coupler instead of a “T”. I very carefully cut a hole in the side of this coupler to be able to pressure fit the tip into it. The silicone air tubing works pretty well, but can be prone to kinking as well as limit the amount of air the venturi can take in. The air stone in this picture is being used as an air filter.

4) The tip. Pay attention to the angles I cut, not just the overall shape of the tip. These tips are normally installed so the point on the end is just off of the bottom of the venturi body for best suction. For more water flow, just don’t slip the tip into the body as deep. For more air push it in deeper.

5) Another angle of above

6) Another angle of above

7) The feed side of the above venturi. Water enters here. It does help to bevel the intake side for a smoother transfer of water between the tubing you will use, and the venturi body. At the top you can see the various tubing I used for reducing the size. This is so I could use the silicone airline.


A Venturi with Bite!

Now for a different take on the same basic idea:

1) Some parts I was considering for making a “toothed” venturi. From this picture I only used the nylon “T “and the ½” aquarium riser tube that just happened to fit into the “T” very nicely. The clear, flexible tubing does not make good tips because it is too soft. Mainly I use it for an air line down to the venturi. The white tubing is stiff enough to make tips from and will resist abrasion well. It is hard to make the back cut on it if you do not have a *very* sharp razor type knife.

2) I tried to represent the depth of the angle on the tubing in this picture in relation to the opening of the venturi body. The clear tubing is “air riser” tubing that is meant for aquariums. It is semi rigid and resists abrasion well. As you can see I sanded a very flat angle onto the end of it. Sanding it flat so it has sharp edges is important to making the tip work well.

3) Same as above, different angle. Notice the depth of the angle on the tip. It is roughly the same height as the hole it will fill once pushed inside the “T”.

4) Shows the tip with one tooth cut into it, installed in the venturi body. This is a good depth to start at with the tip. All I did to pressure fit the tip into the “T” was wrap the tubing with Teflon thread tape. Tip: wrap some on, then test fit, wrap some on, then test fit… Do this until you get it snug, then wrap a few more layers on and fit it again. Teflon tape compresses and may loosen up. If it does, just wrap on some more until it is snug, but you can still adjust it.

5) This shows a close up of the modified tip. It has 3 teeth. Note the angle of the cuts. I used a jeweler’s triangle file to make the triangle cuts. It also makes the back side of the angles nicer. The angle you see in the above pictures were not modified; only sanded flat and de-burred very carefully so as not to round the edges. A sharp xacto knife was used to clean the backside of the V cuts (on the outside of the tube). If the V cuts are clean this will create smaller bubbles than if no V cuts were made. It also provide a longer edge in contact with the water to create more suction. Double Bonus!

6) A good macro of the 3-tooth tip. The white stuff is Teflon Tape used in plumbing to be able to friction fit the tip into the
valve body. You have to put some on, fit it, and then add a couple more wraps and fit it again to make teflon work for you. It compresses on the first fit. The second fit will make it hold better. Oh, I should mention that I have had the best luck running deep with these tips. I think it is because there is more linear edge for the water pressure to act on, creating more suction. You have to have a semi hard material to make this work though, or the teeth will try to fold over on you.

Even a single triangle in the center of the tip will increase the suction. My testing shows this to be a very aggressive aeration design. However, it will plug up easier than a tip that has not been modified in this way. I used this with an
1800gph mag drive pump for a long time before going to a larger version of the same design.

Thats the end of the content in Zik's downloadable PDF, but here is some more information.....

To see pictures of my new venturi based on Ziks design operating in my bio-filter, click here.


Additional Hints & Tips

[These further hints and tips arose from my email discussion with Zik, along with some additional pictures that he took after dismantling one of his venturis for the purpose.]

Dissolved Oxygen

Running at 2 feet or more really makes a difference in the amount of O2 that can be dissolved into the water.

Venturis dissolve more O2 at a greater depth because there is more pressure differential.

Bubbles flowing thru the water give up very little O2 to the surrounding water because of the skin effect water has. The skin creates a barrier at the surface of the bubbles. Bubbles when created or broken will give up O2 to the water. If this is done under pressure (like in a large waterfall) it is possible to supersaturate the water with 02. (Not a good thing, bad for fish).

Venturis allow for maximum aeration without supersaturation of the water, or at least not easy to reach those levels in our situation.

Bubbles that are created at a deeper point will also cause more surface agitation and will circulate the water better in the main body of water if that is where the venturi is used. As far as efficiency is concerned, venturis are amongst the most efficient ways to dissolve O2 into water, when they are designed and applied right. You may wish to look at this page http://home.att.net/~oxymax/aerate.htm as it is very informative.

You wouldn’t believe the amount of aeration you can get from a mag 1800 / 1” venturi combo. Here are some more pictures to look at.

Note the rubber gators over the jubilee clips. These prevent the fish from
rubbing against any sharp edges and hurting themselves.

Venturi Silencers

Note that I did not show any way of making the venturi quiet. We use syringes around here for taking water from the tanks for easy dispensing into the testing vials, so I always have some old ones on hand. I have even used parts of them for use in a venturi. I like to use an old syringe to hold a loosely packed cotton ball at the intake of the air tube. (If the cotton gets wet when you turn off the pump, make sure to toss it and put in a new one). If your venturi is to be used outside, the air-intake pipe and cotton-wool should be protected from rain, otherwise the cotton-wool will get damp and prevent air getting in. Alternatively use some green scouring pad, cut so as to fashion a filter. It doesn't get clogged up when wet like cotton-wool.

Adjustments and Fine Tuning

The tips are adjusted by depth. The tube hanging off of the venturi intake in the second picture is just an adjustable air flow device I had laying around from something else. I think it was made by Marineland for a venturi intake at the output of a power head. (For standard aquarium use).

The further in you push the venturi tip, the more restricted the water becomes, which forces the water through at higher pressure, so causing a more aggressive vacuum on the air, but push too far and the vacuum will have too much air on hand, the water will become a trickle, and the water pump will begin to strain.

The further out you pull the venturi tip, the more water will get through to create a nice current in the pond, but less air will be drawn in to mix with the water.

Adding more teeth to the venturi tip will allow more water through, despite the tip being pushed further into the T-piece. These extra teeth really help the pressurised water bite into the air being drawn in by the vacuum, cutting many more smaller bubbles, and giving more air intake with less strain on the pump.

Cutting the Teeth

When I make these tips out of flexible tubing, I like to use a very sharp (new) blade for an Exacto Knife, and a triangular jewellers file. One of the blades that is my favorite is one sharpened with leather and a very fine polishing powder that is for polishing rocks in a tumbler (final run). If you don’t desire teeth on it, the cut from “sharpening” the plastic tube against some sandpaper gives a good angle and does not need any back side modifications other than removing the plastic flash.

When I make the notches for the teeth out of a hard-plastic barb coupler, I generally use a file and sandpaper, and really take my time so the cuts and angles come out right. I believe that area to be critical to the good formation of vacuum so that air can be drawn deeper.

Before and After a barb-ended coupler has been fashioned using the "tooth" design.

Front Edge of a single-tooth design. Note that the "barbs" have been sanded off on the tip end of the coupler to allow the tip to be push-fitted with Teflon tape.

Back Edge of the single-tooth design.

Push-fitted. This is a good position to start with, giving equal amounts of air and water.

Plastic can be hard to work with because of the flex involved. The toothed design works well as long as you have rigid enough tubing. If the tubing is not rigid enough the teeth will fold over. This type of tip works best where there is no string algae that can reach the tip. The teeth tend to catch junk easily. I do have one of this basic design installed in the outdoor water garden. I use a filter at the intake of the pump to keep junk out of it. I took it apart about 6 weeks ago to see if it was doing ok, and it looked great. Not plugged at all. If you expect gunk to get to the venturi, then just omit the teeth. The back cut I made was nothing more than using coarse sandpaper to get it cut to the correct angle, then using a finer sandpaper to get the edge formed well. In doing this you do create plastic junk at the edge. This will have to be carefully removed with the Exacto knife.

What I do is lay out a piece of sandpaper on the floor. I use the concrete floor in our basement. Hold the part and start working it against the sandpaper. It really gives you a lot of control that way. Just like with sharpening a knife, run the leading edge forward. That leaves the plastic flash behind the leading edge. Easier to remove that stuff from the back side, and less chance of damaging the nice sharply defined front edge, which is the edge that helps break the air/water skin effect.

Choosing Tubing

The tubing that I used for the 3-tooth venturi is “air riser” tubeing from an aquarium store. These are used in the back of an aquarium with a bubbler at the bottom so as to create an air lift. (Water raises with the air, creating an “air lift”). The most common size of tubeing is 1”, but I used tubeing that would fit the part I had on hand. Sometimes the Teflon tape is handy for fitting parts like these. You will have to add wraps, press fit, add wraps, press fit, then add more wraps prior to a final press fitting. Otherwise the part will loosen because the tef tape compresses.

Take the T with you when looking for something to fit inside it. That helps a lot.

Make sure to look at individually packaged syringes too. I buy the kind without the needles on them. Cheaper, and I would just throw away the needles anyway. Here, they are usually packaged in a plastic container with removable end. I have used the outside container if it fits the T.

I like to use rather large tubing for the air intake if the venturi is to be installed under water. This helps to keep the fish from knocking it loose. I have used many ways of attaching the tubing too. I just look at what I have on hand to see if I can make a reducer for a press fit. Between tef tape, and all the sizes of “scrap” vinyl or hard plastic tubeing I have laying around, I can usually find something. I have used all my old syringe bodies too. I had to go out and get a couple new ones anyway. The rubber on the plunger goes bad after a year or so of taking water samples.

These techniques are nothing special, but it did take some work and testing (many hours worth) to get to the current design that I prefer to use. (Basically the design depicted in the last design in the PDF document)."

If you have any comments or suggestions about this project please contact me:

And if you have found these web pages useful and interesting and would like to make a donation, you may do so using the Donations Page.

Alternatively if you have questions you would like to address directly to Zik:

Further Information

I also really like Tim Jansens site which provides some further information on his venturi pages:


Jims Pond Blog

To get the latest news on my ponding bio-filter and venturi experiments why not visit Jim's Pond Blog. You can subscribe to my blog's RSS Feed powered by Feedburner to ensure you get the latest updates. It will work with most Atom and RSS 2.0 compatible news reader software, such as Bloglines, Desktop Sidebar, NewsGator, MyYahoo, etc.


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