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My DIY CO2 Reactor using PVC pipe


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I wanted to share my personal experience with my first DIY project using PVC pipes.  I searched online quite a bit and decided to give it a shot myself.  It turned out to be quite simple, so I wanted to share it here in case anyone else would like to give it a try.


  • 1-1/2" PVC pipe, cut to about 12 inches long (1)
  • 1-1/2" to 3/4" PVC bushing.  Get the one that has threads on the inside (3)
  • 1-1/2" PVC DWV pipe (it's a U-shaped pipe) (1)
  • 1-1/2" Sani Tee Pipe (1)
  • 5/8" hose barb x 3/4" MIP nylon adapter (2)
    • I got the hose barb with 5/8" barb for my 16/22 mm hose
  • 1/4" x 1/2" MIP push-to-connect adapter for the CO2 tubing (1)
  • 3/4" to 1/2" PVC bushing.  Get the one that has threads on the inside. 
    • The CO2 connector goes to that

How I got it free-standing:

I ended up needing to build a stand as well, because the reactor itself won't stand upright. I found a little part of my old computer desk, that had a metal plate and a connected short metal tube (it was meant to hold a small table top that swivels out).  I was able to fit another PVC pipe right onto it and got it to fit snugly by putting a rubber band on the metal tube before putting the pvc pipe on.

Then I cut open a few more 1-1/2" PVC pipes and screwed them into the stand, which clamps perfectly onto the reactor!  I used bolts and tightened it with nuts on the inside, so that it would be more stable and not have a risk of pulling out eventually.  I was really happy to see that I could re-use the PVC pipes to act as a clamp, it made my job so much easier.

Reasons for creating this PVC CO2 reactor:

  1. I am currently using an FZone CO2 inline diffuser, which ends up sending lots of micro-bubbles into the tank.  When I had lights that did not have as high intensity, I didn't notice it much.  However, when I switched to using a higher intensity light, it became very noticeable, and I don't really want to have that 7-up effect
  2. I thought it would be really cool to try and building something using PVC!  It's super fun 🙂

How it works:

  • The idea of the design is that water will be flowing from the top of the reactor, downwards and then out from the bottom
  • The CO2 line injects the CO2 from the top as well, and as the CO2 gets pushed down, it will try to rise up and keep getting flushed down, until it dissolves into the water
  • The idea then is that any water that is able to flow out, should only contain dissolved CO2
  • I decided not to have any bio balls in there, because I won't be able to get in there and clean the media when it eventually gets dirty

As of writing this thread, I have not yet connected it to my filter.  I am waiting on my new filter that will be more powerful (Oase Biomaster 300), so the flow won't be restricted too much.  Once I have it connected, I will update this thread with more information!









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Nice DIY job, but how big is your tank? After running a reactor for a while, I had switched to an inline atomizer, and then switched back to an in tank diffuser. a) because of the added beneficial effect of micro bubbles on plant growth, and b) because any inline contraption over short or long will need cleaning if you want to maintain flow, whether a reactor with, or without bio-balls, or an inline atomizer, or diffuser with membranes, or ceramic discs. I'd rather clean two portions of hose than four whenever I do big filter maintenance. The diffuser is easier to clean too, and the Aquario Neo L from Aquarium Co-Op is doing so extremely well in my 75 gallon tank, that the only way I'd go back to an in-line reactor, or atomizer would be on a tank over 125 gallons.

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My tank isn't big, it's a 40 gallon breeder.  I never actually started with using an in-tank diffuser, because what I had heard was that it's more efficient with an inline.  I appreciate your feedback though, and it's interesting to hear that you're back to using an in-tank diffuser.  It honestly would be simpler to just run a CO2 line into it.  I'll probably give this DIY project a shot anyway and see how it works out, and then decide whether it's something I'll keep using.

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Just a quick update to this reactor.

After building it up (and re-tightened the thread using teflon tape, to prevent leaks, very important step I forgot lol), I ran the reactor for about a day.

My observations:

The good:

  • The flow seemed to be unimpacted with the reactor, as expected since I didn't have anything inside
  • I was getting perfect CO2 numbers based on my drop checker, it's a nice lime green by the time my lights turn on

The not so good:

  • There is a little bit of extra waterfall sound in the reactor itself, I don't think the reactor was fully filled up near the top
  • Without any CO2 in there, I was actually getting a lot of regular air bubbles in the tank
    • This was made even more obvious because I have the Poppy lily pipe
  • With CO2 added, there were way more bubbles than when I was using the inline diffuser, so it didn't seem to fully dissolve the CO2, as intended

End result:

I ended up switching back to my original inline diffuser for now, just to get it back to the way it was.  The reactor was fine in pushing out the CO2 bubbles, but it was not really effective at dissolving CO2, which was the whole reason for building it the first place.

What's next:

There is another design which allows the water to go down in a pipe inside another pipe, and then the water exits from the top of the outer pipe.  Corvus did a video for that design in this video.  I actually thought about doing this design first but I wanted to make use of the 1 1/2 PVC pipes I already had.  I might not do it as extensively as he did, but I am curious if it would work better than the version I tried out.  It was simply a lot of fun building something with PVC for the first time, so I didn't mind that it didn't work out for me 🙂

Again, the goal really was to remove all CO2 bubbles from inside my tank.  Thanks for reading!


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