Venturi Not Working Fluval U2

I'm having trouble with the venturi on my Fluval U2. It seems to have stopped pushing out bubbles. First see the youtube video below. The Fluval u2 is on the left. Notice it's submerged and pushing out lots of bubbles. Mine used to be like this.

See the picture I've attached. The red box is where there's an air intake, so this part has to remain out of the water obviously.

But I noticed that sometimes mine would stop pushing out bubbles. I figured out one day that if the point where the venturi sits into the filter outlet (green box in attached picture) remained out of the water then it would work a lot better. This put my filter up much higher in the tank than you see in that youtube video. It wasn't right but it was working away all the same.

But then the other day it just stopped completely and no amount of messing around could get it to work.

Does any one have any idea what it could be? I've washed out the filter (I do this about once a month - and I did it yesterday), I've taken off the venturi and washed it out and poked a paperclip through it, I clean the pads/sponges regularly (I alternate between sponges - one per week - so each sponge gets done every two weeks). It's not that I have the rubber piece on the top in the off position because I've messed around with that and have even taken it off.

I know that the bubbles aren't necessary and lots of people don't bother with them, but I like the idea of it and I'm happier when it's working.

Any help is much appreciated!!

Thanks
Kevin

Hmm that's a tricky one. A venturi is usually just a very simple piece of pipe that as u can see gets narrow at a point and then bigger. there isn't much else to it.The air is sucked in at the large side and as it hits the narrow passage it will speed up.Up to this point not much can go wrong unless its blocked.Has the filter lost any power? If its not pushing out water at it's proper rate then it might not be strong enough to pull the air through the venturi.Can the venuri be removed from the filter head? if so them maybe the seal between the two is not spot on and water is being sucked in from the tank rather than air from the venturi.Just a few idea's let us know how you get on.

Cheers Stuart.

Thanks Stuart. I don't think it's lost power. Although in saying that, I don't really know. Could be a possibility.

It always created a much stronger flow when the bubbles were coming out anyway and I never really took note of its power when I had bubbles off - just that it wasn't as fast. By the way, I've only had it a few months.

The venturi can be removed at the point highlighted by the green box in the picture i attached.

I had the feeling that the seel mightn't be perfect so, as I said, I discovered that if I raise the filter so that this point is out of the water it seemed to be more reliable.

In fact I've taken the venturi off altogether and just raised it up so that this connection point is above the water. This used to work too except it made a much louder sound than with the venturi on. But now, nothing.

So I've taken off the venturi and poked around in that connection point area. It seems to be clear. I have even covered over the filter outlet with my finger and the water starts coming out from that connection point. So it doesn't seem to be blocked.

You're right - it is tricky!! It should be simple but I can't figure what could be wrong. Maybe filter power as you say. But I don't know how I'd know if that's what it is.

Have you tried cleaning the impeller? This would be the main reason a filter loses power. Just take it out and give it a bit of a clean along with its housing. Use a cotton bud.

Also take off that little cap you have highlighted for this will actually block air!

Hope this helps.

Dave

I think the Bubbles give a false impression that the flow is faster, however, I usually remove the crappy Rubber thing and replace it with a few inches of Airline.

Kev.

Hey Dave - yeah I've cleaned the impeller with a cotton bud.

Dave & Kev - I've taken off both the rubber piece and the whole venturi part and had it so that the connection point (that I highlighted in green) is above the surface of the water. And still nothing.

Any ideas? I've messed around with this quite a lot.

Hi Kevin,

I can't help on this one but I would like to add that I had the very same problem with the same filter.

I never got it to work properly since it started to act up the first time and to be honest I was not that happy with it in general. It is now replaced by an old Eheim (some 20 years old) that works perfectly.

Hope you find a solution.

Melander

Draco wrote:

Hi Kevin, I have its bigger brother Fluval U4, after work I'll see how to solve your problem and I'll let you know what is the solution.
cheers

Thanks Draco. I'd appreciate that.

hi i have the u3 version of this and sometimes it does the same thing,it may have some thing to do with the A,B,C, setting switch on the top,if you go past A, slightly it stops bubbling,i hope this helps

LOL, I love Chris's reply to this post."I'll let you know what is the solution" brilliant.......

Without stating the obvious, is the sponge in the venturi clean? (remove the bit above the red square, remove the little round sponge, wash the sponge under it well (running tap is good)and leave to dry before use!!)
Has the venturi input been turned to max? (where the red square is in your picture) Try rotating the VERY top bit, with respect to the bit between the red square and the green rectangle in your picture. This adjusts the air input. Try removing the cap, if necessary, to check functionality of everything else...

Thanks anglecichlid - I have it in the A position. And I've fiddled a lot with that, hoping that when I put it back to A it might start up again.

Muprh - I've tried taking that rubber piece altogether and have taken off the venturi and cleaned it.

Draco - thanks for having a look. I emailed Hagen yesterday. And they've given me some advice. I'll let you know how I get on. They said:

"To solve the problem,detach the motor from the foam cage and pull out the impeller,clean the magnet and the impeller well.Before re-connecting clean up inside the spray bar on the cage,as this is where the water is pushed up from the motor.

When all is ressembled the filter should work fine.Make sure it is on setting A."

Now, I've already cleaned the motor thoroughly plenty of times. But I don't think I gave enough attention to cleaning inside the spray bar. So maybe there's a bit of a blockage. I'll have another go.

I've also already tried blowing through the venturi with a straw in case that was blocked. Used the lungs. So I'll take out the filter again tonight and have another poke around. I feel like I've tried everything. If this doesn't work then the only thing I haven't tried is p#ssing on the damn thing. And judging by what you've said about it being a piece of junk, maybe that'd be the best thing to do with it!

On that note - recommendations for a good filter? Both internal and external. I'm sure most of you will say just get an external.

Also, what do you have to say about the presence of the bubbles via this venturi system? I like the idea of it, increasing surface agitation and promoting the gaseous exchange. But how important do you guys think this is? I don't mind the noise of it. How does it compare to an airstone?


Thanks for all the help!

Kevin,

I have the Fluval U2 and it gives the same problem.
I can usually get around the problem by taking out the filter media and put the unit in a bucket of tank water and run it without the filter media . Try output through the integrated spray bar instead of the top or bottom output to get it going.
Once you can get the water flow working put the media back in and try again.

I agree that this product is dissapointing. I have since stopped using it and it is in the shed.
I purchased a second external filter for the tank and used the spray bar for good water surface movement.

I'm using the JBL CristalProfi external filters . I have a E1501 Greenline( 43% less power usage than the old E1500 model) and e900 which are excellent. The flow on the E1501 is very powerful.

Greg

Hi i just said I'd get back on and let you know how I got on. Seeing as I know others have issues with this filter too.

I have it working now. The bubbles are streaming out like they used to.

Things that can cause problems:

1. The filter is not on setting A.
2. The rubber cap on top of the venturi valve is not letting air in.
3. The point where the venturi valve connects to the outlet nozzle is blocked.
4. Loss of power of due to blockage somewhere.

Solutions:
1. Is obvious.

2. Just turn the rubber cap. Or remove it altogether. Or just let it sit loosely on top.

3. Take off the venturi valve and clean it. The point of connection is tiny so it could easily get blocked. I've now just taken it off an replaced it with a small pipe.

4. This requires a thorough clean.
4.1 Take off the motor and remove the magnetic impeller. Clean inside this area with a cotton bud or something.
4.2 Clean up inside the spray bar. You can just take out the filter media and leave it sitting in some tank water. Then run some water through the spray bar at high pressure. You could shove a pipe cleaner or something up around it too.
4.3 The middle section that contains the ceramic rings needs to be free of slime that builds up. Especially at the bottom of this cartridge because water flows through here.

It was 4.3 above that was mostly causing the problem for me. I had looked at every other aspect but I didn't really touch that part very often. Only now and again I'd shake it around in some tank water after a water change. But I never really opened it up and dug out some of the slime. I think it was blocking the flow a bit, causing it to be slower and not having the power to draw in the air. I think this is also the reason why I had to have my filter up quite high in the tank to get any bubbles going - the lower down the filter is, the more power it takes to draw in air (as far as I can tell).

Anyway, thanks for everybody's suggestions! Hopefully this has sorted it out once and for all.

Hi Kevin,

excellent update could be worth posting as a topic on its own given that this issue will come up for most people using the Fluval internal filters, or any internal filter with a venturi for that matter.

Cheers,

Bill.