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How To Use A Venturi In Your Fish Tank or Aquarium

Updated on October 11, 2009


How To Set Up A Venturi

  • Connect the tube to the appropriate outlet point.
  • Ensure that the outlet point is connected to the filter and that the venturi outlet is vertical.
  • Hang the head of the venturi outside the tank.

Et voila! Additional oxygenation!

Let's start this hub with a confession. I owned and ran an internal filter for many months before I worked out what the little piece of plastic tubing with the doodad on the top was. It was, they said, a venturi. But what was I supposed to do with it? The plastic tube went into a little outlet pipe for the filter, I could work that much out, but then what happened?

At first, I assumed that the water bubbled up through the pipe somehow and made bubbles on the surface of the water. So I tossed the venturi in the tank, connected it all up, and swore at it when it did nothing but float there limply on the surface of the water.

There is very little information out there about how to use a venturi. The best I could get by googling was a multitude of results for fish tank filters that included venturis. Not very useful as I already had my venturi and it didn't do anything at all.

It wasn't until I found the need for extra oxygenation in my tank (with the addition of a chiclid, after keeping Bettas, who breathe from the surface of the water and can get by with minimal oxygenation in their water,) that the venturi issue came up again. This time I found answers.

What Is A Venturi?

A venturi is a simple device consisting of a tube which is narrow in the middle. In most aquarium venturi's the plastic nozzle at the top contains the narrow point. When a flow of water is applied to one end of the tube, it creates a vacuum, sucking air in from the outside world. The air mixes with the flow of water, and in an aquarium, bubbles to the surface. A venturi is simply a device designed to oxygenate a flow of water.

How Does A Venturi Work?

Now I knew what the venturi was for and how it was supposed to work. You don't let the head of the venturi rest on the water, you hang it outside the tank. Once again I puzzled at it, sticking it into my filter as before, and once again, it failed to work. Now it hung limply outside the tank, whilst, under the water, the current was undisturbed.

Like a cave person investigating a strange phenomenon, I tried breathing down the venturi tube. At once, many tiny bubbles poured out of the filter. Success! But limited success. At present time my life does not allow me to spend all my days breathing down a tube next to my aquarium.

Assuming that it was broken, I twisted the bottom of the venturi, by the filter, turning the little nozzle to an upright position, lo and behold! It sprang into action, with thousands of bubbles merrily making their way to the surface of my tank, oxygenating the water.

And that's how a venturi works.


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    • profile image

      Laurie English 

      7 months ago

      You brilliant bugger. I sat looking at this Venturi? read your spiel and became an instant expert. Thankyou.

    • profile image


      4 years ago

      Up to this day I never knew what that was for either but today I brought a 60 litre tank and the filter came with a venturi that works at the push of a button so I googled to see what a venturi actually does and saw this post .

      I went over to my original 20 litre tank and tried to turn the switch but still nothing happened so I blew in to it as suggested and a load of slime come out of it then hey presto I had bubbles so thanks for finally letting me know what it is shame I never googled it before as wont be using the small tank once the big one has cycled

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      5 years ago

      I just bought a pump with the venturi, was having problems with getting it to work (water kept backing into the pipe) then i figured out why this was happening. If you put the Venturi connection too far down in the tank, the water pressure from the outflow causes water to back up into the tube, if you move the venturi junction (the place where the plastic tube connects with filters outlet) closer to the surface, the pressure gets relieved and you get bubbles like there's no tomorrow.

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      6 years ago

      I've recently bought a second hand tank complete with filter, I assumed the tube went into the tank, and fitted to a fountain device/ornament, when it wouldn't attach just though it goes in the tank. I found this earlier, so understood it dangled outside the tank, and the pump is fully submerged. The tubing attaches to the narrow pipe (facing up as the picture) and the air comes out of the wide pipe into the water, it's quite powerful (for the lowest model) and if the fish are still the get dragged backwards slightly, but I'm sure they'll get used to this. The venturi makes some noise but this could be as I'd got water in the tubing earlier.

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      7 years ago

      I just inherited a 5ft tank with all equipment but unfortunately no boxes for any of the gear. Google gave me instruction manuals for most of the stuff but I had NO idea what to do with that tubey thing....

      THANK YOU for providing such a simple explanation without making me feel like a total moron. Very much appreciated. lol!

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      7 years ago

      Just thought I would share how I fixed my filter.

      The plastic tubing attaches to a plastic cylindrical spike that fits into the top of the outlet (the place where the water is pumped out). This cylinder fits into the outlet about halfway. Now, disconnect the pump and look into the outlet. You should see the lower half of the cylinder coming through. The bottom of this cylinder is not cut off straight it is diagonal. From the side the bottom of the cylinder will look like this | | . Rotate it until the open bit is facing forwards. \| Hope that helps someone.

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      7 years ago

      is it redundant to use the venturi with a waterfall? I have a reptile-clear 250 that comes w/ an aeration device, but the outflow us set up as a waterfall (in a aqua-terrarium that holds freshwater amphibians).. Since the water is hitting air as it falls from the tubing, is it pointless to use the Venturi, or could provide a benefit? Many thanks for your help...!

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      7 years ago

      The venturi only works one way.. if water is coimg out the top, put the nozzle the other way in at the pump

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      7 years ago

      You are my hero.......i was also like you and threw it into the box as a spare part, but now with confidence i will use it!!!

      Ant my fish want to thank you too!!

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      7 years ago

      @Hattori: Basically it means that make sure the nozzle and the tube that attaches to it are upright, and out of the water, and that everything is fitted VERY snugly with each other. If you're still having problems, try squeezing the tube only where it connects with both the little round knob at the top (the thing the sucks in air) and where it connects to the nozzle (which is in turn connected to the filter).

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      7 years ago

      Hello! I'm sorry, but I don't understand the following: "Assuming that it was broken, I twisted the bottom of the venturi, by the filter, turning the little nozzle to an upright position... " I have the same problem. Can you, please, explain more about how did you make it to work? Thanks a lot!

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      7 years ago

      you need to make sure your filter water outlet is not blocked, if it is blocked water will come out of the venturi, and eventually break the pump

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      7 years ago

      Works fine many thanks

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      7 years ago

      i have a venturri tube like pictured above and all that happens with it is water comes out the black plastic bit on the end can u help??

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      7 years ago

      Hi I did this and all was fine for several days! However water now seems to be coming out of the tube and I can find no explanation anywhere! Help

    • profile image


      8 years ago

      Excellent! I, like you, have been in the dark and wondered how well the tank was being oxyginated. Even the local fish suppliers did not pick up on it when we have had issues. He just said run the pump on max flow through.

      Many thanks from me and expecially our fish who are now breathing a big sigh of relieve!


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