Replacement Flow Tube for Fluval Spec Aquariums (III and V)

When I wrote my page on replacement parts for Fluval Spec aquariums, I had pretty good success finding sources for most parts. The one mystery was where to get replacement hose for the flow tube.  Some people who were interested in the flow tube modification were concerned that if they botched the job a replacement would be in order.  It is not a hard mod, but I wanted to put people at ease and I set out to find a good source for replacement.  However, this has turned out to be a bit harder than expected.

food grade silicone tubing as candidates for fluval spec aquarium

To back up one step, the part in question is a little rubbery tube connects the pump outlet to the elbow at the flow nozzle.

I will cut to the chase and give you the only source I know of for an exact replacement.  A very kind reader reported that if you order the output nozzle from Hagen’s website, they include a replacement flow tube.  This isn’t clear from the product description, and I haven’t confirmed this myself, but that is what the good readers report.  This is great news.  It is not that expensive (shipping cost much more than the part) and it is a direct and exact replacement in size and material.

fluval spec aquarium replacement nozzle with silicone flow tube

The real fun is in finding a source for hose on your own.

Replacement Flow Tube Hose – What to Look For:

The basics is that you are looking for Food Grade Silicone Tubing.  This is the material used for the part.  Food grade implying that it is safe for use with your fish.

The real fun comes in finding what size Fluval uses with their aquariums.  Hose is sold in various sizes.  The size is indicated with two numbers.  The first number is generally the inside diameter.  The second number is the outside diameter.  The food grade silicone tubing is here is a rundown of what I have tried and how it fared.  (click on image below to enlarge)

silicone tubing with notated inside and outside diameters for fluval spec aquarium

  • 9mm ID x 13mm OD:  A reader suggested this and seemed to think it fit.  I don’t know how he or she got it to fit.  The inside diameter seems entirely too small to fit over the fittings at the pump / elbow.  Next!
  • 1/2″ ID x 5/8″ OD: I did some conversions from metric to english and it seemed a 1/2″ ID hose would work.  Technically, it does work.  The wall thickness seems to match; however, the ID is a bit larger than the stock hose.  Bottom line is that it works – it’s just not exact. I would be a bit worried long term that it will loosen and not hold tight over time.

At this point, I decided to contact Fluval and ask them about the hose.  Here is their response:

Dear (Spec-Tanks owner guy),

We thank you for taking the time to contact us.

It is 7 3/8″ long the ID 3/8″ OD 9/16″.

Thank you,
Elaine Boyce
Customer Service Dept.
Rolf C. Hagen (USA) Corp.

So here we go – getting somewhere!  Off to get the size they describe.

  • 3/8″ ID x 9/16″ OD:  Still doesn’t match!  Wall thickness is thicker than the stock and the inside diameter is slightly smaller than stock.  It does work but is a little bit tighter to fit over the fittings.

So where does that leave us?  For metric, I’d guess the correct size is something like 11mm ID x 14 mm OD. For english, a best guess would be 7/16″ ID x 9/16″ OD.  I’m done hunting down hose for the moment.  If you don’t want to get the Hagen flow nozzle part that comes with the hose, I would suggest sourcing 3/8″ ID x 9/16 OD as it is the best function and fit of those that I have tried.

food grade silicone hose

22 thoughts on “Replacement Flow Tube for Fluval Spec Aquariums (III and V)

  1. Thank you SO much for this information and the link!!! I lost the bend that goes from hose to the output nozzle. I suspect my cat stole it for a toy. I also needed a new tube as I got a bit too enthusiastic with cutting some holes to slow the flow for my betta. I have 2 Spec Vs and 2 Spec III tanks so I’m going to love reading through your journal. You saved me tons of searching. I’m also interested in your mods.

    Thanks again,

    1. Jane,

      Did you order the part? If so, did it come with a replacement hose?

      1. Yes, it blessedly came with a hose. I was trying to reduce the flow and cut too many holes in my hose, so losing the nozzle was a blessing in disguise.

      2. Yes, it did come with a hose. Lesson learned – when reducing the flow, never cut too many holes in your hose and you won’t need a new one. 🙂

    2. You know, you can reduce the flow by pulling the pump “it has suction cup at the bottom” on the pump there is a switch you can push side to side. Increase and decrease.

      1. The lowest setting doesn’t make the flow low enough for my betta unfortunately.

  2. They will send you the tube for free… they sent me one

    1. It will interchange with the V. I took the nozzle that came from a new III and put it on my V just the other day. Works fine.

  3. This article was incredibly helpful to me. I keep a beta in a Spec III, and I cut too many holes in the original tube. This post saved me hours of research and a lot of frustration in finding a replacement tube. The Hagen site was sold out of nozzles, but the 3/8 ID did the trick. Thank you!

  4. has anyone tested the tube with just the Fluval pre-filter capping the output to see if that reduces the flow enough that you don’t have to ventilate the tube?

    1. I don’t think I have tried that combination. I mainly put holes in the tube out of necessity (better heater performance). You should try it – I think the combination of Fluval Pre-Filter and turning down the pump volume (with the pump’s slider) would get you in the ball park of what you need.

  5. What are the inner diameter of the outlet nozzle and the elbow if any one has it?

  6. Found the A14654 output nozzle on amazon for around $15. It includes a hose. Any other ideas about reducing the flow to protect a betta without trial and error punching holes?

  7. I can’t thank you enough for all this information on the Fluval spec (19 litrs) I have just bought the latest version with honey comb effect to hide filter (Jan 2020). We have now performed the hole drilling x 5 and I found that I needed to put lever half way on flow control. The flow is perfect for my Betta and uprooted pants(dwarf Sag) just gently move around.
    My next question about the Spec is the lid. I have covered the slit with dressmakers net stuck with cellotape as a temporary fix. I do not want this chap to jump out as I waited a long time for him. he is a Betta Imbellis, absolutely gorgeous, from Frank’s Bettas. I am thinking of getting glass cut and buying the runners like my Aquanano 40 has. He needs a moist air layer as he is a labrynth fish like all bettas are. I wondered if the long hole on the supplied tank was reducing/removing the moist air available to him?

    The D and D mesh is fab but very expensive for the amount I need but would not retain the humidity? Any thoughts re a lid for a Betta. I am settling down now to read all of this Blog!

    1. 1. Awesome about the flow mods – glad they worked for you!
      2. Sounds like an awesome fish! I haven’t thought about covering the center opening. Netting or screen material would be fine – perhaps hot glued in place(?). I really don’t know about the ‘moist’ layer he requires. that is a new one to me. On the other end of the spectrum, if you seal it up too tight, you might hurt oxygen transfer.

      Sorry that I’m not much help, but I bet you will come to a good solution.

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