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CO2 Connection/Plumbing Questions


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I have Googled and Googled but can't find these answers! Hopefully y'all can help. This is for a DIY citric acid/baking soda system, but I assume the fittings and connections are the same. 

First question, can the solenoid be placed after the bubble counter? I have a solenoid on the way, but it is configured to be inline, so can the system be setup: 

needle valve > bubble counter > 1/4 in tube > solenoid > 1/4 in tube > check valve > 1/4 in tube > diffuser 

If not, second question. What is this fitting called?! I can't find it anywhere. I know it's a 1/4in OD compression fitting and the threads are 3/8 in, but I haven't seen anything like it in hardware stores. The compression fittings I have seen are different, no o-ring on the male fitting. 


This is setup to thread on a bubble counter with the o-ring, or for airline/co2 without the o-ring and the threaded compression collar. I'm trying to figure out if I can change the fittings on the solenoid to connect it between the needle valve and bubble counter. And if not, can I adapt the bubble counter to be inline using a 1/4in compression coupler: 

needle valve > 1/4in tube > solenoid > 1/4in tube > coupler > bubble counter > 1/4in tube > diffuser 

This is the only type of compression coupling/union I can find. It looks to have a barb, but no o-ring placement to seal the bubble counter onto. None of the pictures show without the compression nut, so I can't see the threads. I haven't had a chance to just run to Lowe's to look at one in person.  


Thanks everyone! 

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On 1/23/2023 at 12:02 PM, A3M0N said:

needle valve > bubble counter > 1/4 in tube > solenoid > 1/4 in tube > check valve > 1/4 in tube > diffuser 

I'll try to dig up some details and attempt to help out.

The way mine is setup (regulator) everything is after the solenoid.  Needle valve and everything that follows is after the solenoid.  This probably stops some of the muck / junk from getting in there too.  Might just be a design flaw or intentional given the different technology.  (I would imagine the solenoid getting gunked up isn't a good time either and you gas out the tank.


Photo of DIY CO2 using baking soda and citric acid.

First.... a bit of a history of this guy....

Aquarium DIY CO2 Generator System Kit CO2 Generator System with Solenoid Valve Bubble Diffuser Carbon Dioxide Reactor Kit for Plants Aquarium product image 1 of 4 slides

It's sold by a LOT of different brands and it's sold in a variety of configurations.  The real reason that valve/solenoid is in that location is because the crossbar+needle valve is something that is a "completed design" and that assembly is basically adapted to whatever product line you want to choose.  Similar to how you can have your own "algae wafer" and slap your youtube channel on there and call it a day, or other products that are designed, sold to manufacturers, and then packaged under that brand / umbrella with their specific design/packaging requirements.

That's the... quick way to explain that.

In terms of placement and setup, with the kit you have.... That's the setup.  Things like having tubes and length of tubing are searched online and are used as a means to keep the equipment clean.  That might be something to look into and might help keep the valves clean for you.  Right now, every time you add more stuff in, I'd clean it just to keep things going.  I had to do the same junk when my Tidal stuff was going bonkers and the tank was fighting me with algae and plant chunks in everything.

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Thanks for that info. I didn't buy the same brand solenoid as my kit because it didn't have very good reviews. The one I got has good reviews but is configured inline, so I bought it and decided I'd figure it out.

I still don't know exactly what kind of fitting that is. Is the same on "real" co2 systems? Like how the bubble counter is mounted? The best I found so far was one webpage said some compression fittings have o-rings, if not thread tape can be used for a seal. Maybe I'll just run to the closest hardware store tomorrow and see what I can see. 


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Well, this topic is kinda moot for me now. My new diffuser doubles as a bubble counter, but it wasn't working very well as a bubble counter - fantastic diffuser though. Now after running for a couple days and getting more water inside it's working great. So I can ditch the bubble counter I have and run the solenoid inline with no issues.

However, I'd still like to know more about the fittings for future reference. I'll keep looking here and there. 



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