Persistent Bubbles in Neptune DOS Tubing After Fitting Upgrade

[Salahunreal]

I’ve been trying to upgrade the fittings on my DOS setup and wanted to check if anyone has run into the same issue.

I swapped the original DOS fittings for quick‑connect 1/4"–1/8" ones, removed the nipple on the DOS head, and used Teflon tape on the threads. Even so, the connection wasn’t airtight and I started getting bubbles in the line.

Later I learned that the tubing I used was actually airline tubing, which doesn’t seal properly with these types of fittings. I was advised to use the 1/4" (6.35 mm) push‑connect down to 3/16" for the airline tubing.

I’ve now replaced the intake with RODI tubing and kept the output the same, but I’m still seeing bubbles forming.

Has anyone experienced this or have an idea what I might be missing? It’s starting to affect my alk dosing, so I’m trying to get this sorted out.

Does anyone have an idea what I might be doing wrong? It’s affecting my alkalinity dosing, so I’m trying to find a reliable solution.

Appreciate any feedback

 

[jonelder68]

What brand of push lock fittings? Cheap ones/amazon ones have always caused me issues. I only use Murdock or John guest only now.

Did you cut the end off the Dos fittings below the threads?

 

[Salahunreal]

Just cheap copy of those. Not easy to find it in Sweden.
Yes I did cut the grey nipples also

 

[jonelder68]

I would suspect fittings issue. Sometimes different brands of fittings don’t pair well also. If the barb/stem fitting is a different brand than the 1/8”npt to 1/4 pushlock?

Sorry not much help but hard to diagnose remotely. Try switch lines around and see if bubbles follow? Process of elimination is your friend here.

I’m sure you primed the lines? Mine took like 10 minutes straight to fully prime

 

[Salahunreal]

Thanks for your help. Appreciate it.
i guess yes it is the fittings, I found a store where I can buy the john guest fittings in Lativa and they ship to Sweden. so might order it from there. Yes I have primed every time I change any fittings and I do calibrate to make sure all in check.

 

[bushdoc]

I had same problem, tried different fittings and tubing and it eventually worked, but overall I was not very happy with the brand and I am running different dosing pump now without any issues

 

[Salahunreal]

I had same problem, tried different fittings and tubing and it eventually worked, but overall I was not very happy with the brand and I am running different dosing pump now without any issues

Which brand you wasn't happy with?

 

[Gudhjem]

The challenge with this mod is that the male threads on the grey dos fittings are not pipe threads. Pipe threads taper and form a seal as they are tightened. The parts don't actually screw all the way together and the joint tightens before that hapens. Non-pipe threads are meant for fastening, not sealing. You can sometimes fudge it by using pipe thread or pipe dope, but it's challenging to get this to not pull air. Neptune's decision to not use pipe thread in this application is perplexing. Design-wise it seems such an obvious choice and would have avoided hundreds of problems and dozens of threads like this one on this forum.

Hopefully someone crafty with a 3D printer will print a part that matches the grey DOS fittings, but uses NPT threads, which would solve the problem.

 

[Salahunreal]

The challenge with this mod is that the male threads on the grey dos fittings are not pipe threads. Pipe threads taper and form a seal as they are tightened. The parts don't actually screw all the way together and the joint tightens before that hapens. Non-pipe threads are meant for fastening, not sealing. You can sometimes fudge it by using pipe thread or pipe dope, but it's challenging to get this to not pull air. Neptune's decision to not use pipe thread in this application is perplexing. Design-wise it seems such an obvious choice and would have avoided hundreds of problems and dozens of threads like this one on this forum.

Hopefully someone crafty with a 3D printer will print a part that matches the grey DOS fittings, but uses NPT threads, which would solve the problem.

Thanks a ton for this detailed explanation. Now it is totally clear and I will stop buying different 1/4-1/8 adapters as I thought it is matter of quality.

I like your suggestion to print it but how? I have designed my own COR20 guard that will thread on the inlet and I do design sometimes like one time I did an inlet guard for my COR20 and was trying to find the correct thread and so and got it eventually with the correct thread but not sure how to do it.

I mean the thread part it should not be an issue and will seal but I doubt that making the push fitting part itself as a 3d print will be good idea.

 

[areefer01]

Thanks a ton for this detailed explanation. Now it is totally clear and I will stop buying different 1/4-1/8 adapters as I thought it is matter of quality.

I like your suggestion to print it but how? I have designed my own COR20 guard that will thread on the inlet and I do design sometimes like one time I did an inlet guard for my COR20 and was trying to find the correct thread and so and got it eventually with the correct thread but not sure how to do it.

I mean the thread part it should not be an issue and will seal but I doubt that making the push fitting part itself as a 3d print will be good idea.

That is slick. What material / filament did you use if you don't mind me asking.

Also does that cause any cavitation? I know when I was talking to Royal Exclusive they recommended extending the intake with the grooves and/or holes instead of the shorter, more compact approach like you have here.

I am using one of the intake covers from BRS (US) but it is very restrictive. Needed though as I have strombus snails that get sucked up in the intake :( Never thought about 3d printing something.

 

[Salahunreal]

Thanks! I used Bambu Lab PETG for the filament. I went with PETG because it’s widely considered reef-safe and handles the saltwater environment without breaking down over time.

As for the flow and cavitation, I haven’t had any issues at all. I actually have two of these running—one on my skimmer and one on my return pump—and both have been performing perfectly with the intake guards attached. The flow remains steady and the pumps stay quiet!

 

[areefer01]

Thanks! I used Bambu Lab PETG for the filament. I went with PETG because it’s widely considered reef-safe and handles the saltwater environment without breaking down over time.

As for the flow and cavitation, I haven’t had any issues at all. I actually have two of these running—one on my skimmer and one on my return pump—and both have been performing perfectly with the intake guards attached. The flow remains steady and the pumps stay quiet!

Thank you. I will check that filament out.

I actually run 2 x Cor 15's and 1 x Cor 20. Since they are all the same body should I need to take one off line I can switch between them without any plumbing changes.

 

[Salahunreal]

Thank you. I will check that filament out.

I actually run 2 x Cor 15's and 1 x Cor 20. Since they are all the same body should I need to take one off line I can switch between them without any plumbing changes.

But the driver for COR 20 isn't the same, right? If you have the COR 15 and replace it with COR20 then you need to change the driver as far as I know.

 

[areefer01]

But the driver for COR 20 isn't the same, right? If you have the COR 15 and replace it with COR20 then you need to change the driver as far as I know.

Correct, the driver is not. The Cor 20 has an additional power supply which gives it the additional 500 gph. The Cor 15 does not have this.

The bodies, and connections, are the same. So if one of my pumps needs cleaning, or something is wrong (I've had strombus snails get stuck in the volute/spiral casing), I can take my skimmer offline, remove the working pump, swap it with any of the others, and it will work fine.

Drivers stay where they are. I'm just moving the bodies around since the connections are all the same.

 

[Salahunreal]

yeah I have two COR20 and one COR 15 as a backup for similar cases as you mentioned.