Help with Fluval 306: flow reduces to nothing after hours/noisy

Hi everyone,

I would like to hear your advice and thoughts about my Fluval 306 canister filter which is being incredibly frustrating! I just bought an established tank that came with the filter. I am a returning fish-keeper - I used to have them as a teenager but that's been a while. So, the filter works fine when first set up. The flow is great and creates quite a current in my tank (29 g, sand substrate, planted) but after a few hours it starts to reduce to the point where there is really only a small trickle coming out of the outlet after overnight. It also makes a gravelly noise. I have cleaned everything really well and multiple times and cleaned and greased (vaseline) the O-rings on the top and on the Aquastop inputs and also the impeller and shaft. I have also primed and shaken the pump to try to get any trapped air out. Note that there are NO air or microbubbles in the outlet water.

If I unplug, remove the Aquatstop completely, turn back on, the flow returns to normal BUT then reduces as described. Noise is still there.

Some things I have noticed:
- When I remove the Aquastop or move the lever a lot I do get a water droplet at the side on the grey... circle thing. Sorry, don't know the name but it's like the 'wheel' of the lever. Have attached a photo. It's beading because of vaseline on there. A few drops come out only when I move the grey aquastop lever and it's not much.
- The impeller cover appears to be warped. I don't know how much of an issue this will be
- Priming does NOT return flow to normal

ALSO on a side note, on first cleaning a little rubber stopper thing fell out! No idea where it goes. Any ideas? Attached is a photo of it alone with the flow
Hope to get some help! I am getting super frustrated with this thing!

Some photos attached: the 'mystery part', flow after 6 hrs/overnight, flow AFTER removing Aquastop and refitting (it then gradually returns to slow after 6 hours or so), leaking Aquastop

Hi and welcome to the forum

The most common cause of noisy external canister filters is air being drawn in somewhere. Normally it is the o-ring and smearing a thin layer of Vaseline on the o-ring fixes the issue. In your case it hasn't. You do have water dripping out from the aquastop?, which would indicate it is leaking and possibly air is still causing the problem.

You do not need Vaseline on the impellor or impellor shaft. The shaft should be clean and free of foreign matter to prevent premature wear.

Check the impellor blades and make sure they don't spin all the way around. To do this, hold the magnetic base of the impellor and gently turn the plastic blades with your finger. The plastic blades should only turn so far and then stop. If the plastic blade turns all the way around while you are holding the base, then the impellor is stuffed. This is probably not the issue.

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The rubber grommet is probably from the impellor shaft. They normally have 2 grommets on the impellor shaft. One grommet sits on each end of the impellor shaft and there is usually a groove in the pump housing and in the round impellor cover where the grommet fits and holds the shaft in place. If the impellor shaft does not have both grommets, it could move and stop the water flowing properly.

The grommet in the pump housing does not always come out easily and might still be in the pump or it might be the one in the picture. You will need to shine a torch in the pump housing and see if it has a grommet for the impellor shaft.

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The aquastop thing you mention looks like a tap. These are meant to be used when you clean the filter but in my opinion, are useless and pointless don't help at all. Leaking taps can cause air to be drawn in and stop the pump working properly.

Primer mechanisms on canister filters are in my opinion pointless and useless too. The best way to start an external canister filter is to have the filter set up with the intake hose in the tank. Have an empty bucket next to the canister filter. Suck on the end of the outlet hose until the water starts draining into the filter and then put the outlet into the empty bucket next to the filter. Allow the filter to fill up and wait for the water to flow freely into the bucket. Then put your thumb over the outlet and put it in your tank. Then turn the filter on.

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You could try removing all the filter media and internal fittings and see if the filter runs normally without them. Just put the filter media in the tank or in a bucket of tank water and have an airstone bubbling away in the bucket of water. Then see if the problem continues. If removing the media fixes the issue and the filter flow remains normal, then put the filter media cages (without filter materials) back inside the filter and see how it goes over 24 hours. If it's still good, then put one lot of filter material in the bottom media cage and run the filter for 24 hours. If it's fine with that then put media into the middle cage, and so on.

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If the impellor has both grommets and there are no water leaks or air being drawn into the filter, then the only other cause is a faulty motor. It could be over heating or just have a faulty circuit, however Fluval motors are usually pretty good. So check the impellor grommets and remove the aquastop/ tap if you can and connect the hose directly to the filter and see how it goes.

If you believe it is the motor, take the filter to your local pet shop and ask if they have a second hand filter or motor that you can try. Ask if you can leave your filter running (with their motor) at the shop overnight on one of their tanks and see if it still happens. If it continues to be an issue with one of their motors then we go back to looking at o-rings and grommets

If you do take the filter to a shop and leave it over night, do not take the filter materials with it, just leave them at home in the tank. That will stop any diseases contaminating the filter materials.

That grommet looks a bit too big for the impeller shaft to me but I could be wrong.

Have a look at the manual and see if it looks like anything on it.

http://www.fluvalaquatics.com/media...a212-a217_06-filter-series_manual_na_2014.pdf

It actually looks more like one of the feet?

As Colin says, it could be the motor or it could be the impeller itself. I also don't like the sound of it when you say you have a warped impeller cover. That doesn't sound right to me.

You could also try asking Fluval directly what the problem might be.

http://www.fluvalaquatics.com/ca/faq/

Thank you both. Yes, I think it's way to big and I just chatted to them on the phone and they don't think it's from the impeller, there is just no room for it. But I will check again when I install the new parts. I am trying to avoid taking it apart too many times right now. The lid is pretty tight and hard to remove, which I suppose is a good thing.

Colin, thank you for such a detailed reply! Thank you for taking the time to write all of that. I am out right now but will re-check the impeller. From memory I am 99% sure it can only turn right and left about 45 degrees before it stops. Once I get the replacement parts (see below) I will follow all of the steps you suggest.

There is no water dripping anywhere but occasionally I find a drop of water beading on the aquastop. From the fact that when I take that part off and put back on fixes the problem temporarily makes me think it is the aquastop.

One more question: if there is air leaking in, won't I see small bubbles in the output? I don't see this but since there is no water dripping I suspect any leak is pretty tiny.

Update: they have agreed to send me the two replacement parts (impeller cover and Aquastop) so I will update when those arrive and see if it fixes the problem!! Took a little convincing but they were friendly and helpful and are sending them free of charge.

If there is a small air leak, the air will usually get trapped in the impellor area and doesn't normally get pumped out. This air can slow or stop the impellor spinning because the plastic blades have to turn against air and water and it can stop the impellor spinning.
The air around the impellor can also cause the motor to heat up because they rely on water flowing through them to stay cool. If the water flow is reduced due to air around the impellor, there is no water to cool the pump and it will heat up.

If there is lots of air being drawn in you usually see a wet spot on the floor where water is leaking out of the filter and you get air coming out of the outlet hose.

If the filter is new from a shop, there is a possibility that one of the staff had taken some parts from it to use on another filter or sell to a customer, and the replacement parts are not for that specific model. This would explain the large odd shaped grommet in the photo and possible bent impellor cover.

O-rings should be tight but not excessively tight. Again if that is the wrong o-ring, it could be leaking from there.

have you checked the inlet to the filter in the tank, whenever mine got blocked it reduces the flow and gives the gravelly sound as it isnt getting enough water to pump

Thanks again for the help! Some updates:

I found the mystery part! It's a foot
https://usa.hagen.com/Aquatic/Replacement-Parts/A20119

I called Fluval and they have agreed to send me a new impeller lid and Aquastop. This was a nice surprise and they needed a little persuading since I didn't have proof of purchase, but I am super happy with them. Once I install those parts I will post the outcome. Once again this morning I woke up to find the filter barely pumping. Unplugging and replugging in the Aquastop made some of the flow return but not all.

Regarding the intake - it has a different set up. Just a foam sponge like this:


(pic from online, not mine). Note that the sponge just fits over the black pipe with the white end - there is none of the original clear tube. This does get a bit clogged (the base gets sucked up) BUT I don't think it is restricting the flow too much since cleaning does not do anything by itself. But I am wondering if I should go back to the original set up. The intake sits about 4 inches below the surface.

I wonder if I should remove and replace with a DIY strainer, perhaps some netting and a elastic band? Just a thought

Just another thought. If you turn the filter off and then back on again, without removing the aqua stop does the flow improve?

seangee said:

Just another thought. If you turn the filter off and then back on again, without removing the aqua stop does the flow improve?

Click to expand...

Not really. I saw one suggestion which said to unplug and replug rapidly a few times but it didn't seem to do anything

Can you post some pictures of your intake strainer?

If it has a sponge on it, then the sponge might be blocking up or restricting flow and that might be the issue.

if the sponge is pulling up when running then the flow is getting restricted a bit, try it with the original intake if you dont have fry and see if the same happens

I have one of these on the intake pipe for my 406 (I don't use an air filter - it just fits over the tube). Never had a problem with the flow. Added benefit is I have a ready cycled filter for when I need a quarantine or hospital tank.

Colin_T said:

Can you post some pictures of your intake strainer?

If it has a sponge on it, then the sponge might be blocking up or restricting flow and that might be the issue.

Click to expand...

Here is the intake, along with a photo showing the location. I am getting super frustrated. Today I came home (from first day at new job) to find a mere trickle from the outtake. I took apart and reassembled and it's still awful. Sigh. New parts don't arrive until Tuesday

You might have a dodgy motor that is heating up and reducing the flow. However, try to deal with it until Tuesday and try the new parts. If they don't fix the issue then see about getting the motor swapped.

As long as the water is still flowing through the filter, the bacteria will be fine. Just keep the feeding down for a few weeks until this matter is resolved.

You could take the impellor to a pet shop and see if it is the same size as the ones in their filters. An incorrect sized impellor could cause issues.

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In the picture you provided, the intake is only a few inches down from the top. Normally you have the intake tube lower down in the tank so it draws up water from closer to the bottom of the aquarium. This allows the filter to pick up more gunk and provide a better turn over of the water in the tank. Basically you have the intake near the bottom (not too close due to the sand), and the outlet blowing across the top. Clean water goes in the top and dirty water is taken from the bottom.

Where the intake sits is not going to cause the problem with the flow rate but you should try to have the intake a bit lower down

Thank you Colin! I will move it - looks like I will need to get the intake tube thingy since the pipe is already cut short

If the new parts don't fix it I'll look into the motor. Fingers crossed...