Horizontal CO2 Reactor - Yugang 鱼缸 Reactor

[ScaperHaynes]

Thanks for the input. I'll order a CO2 test kit just for curiosity and report back. Yeah, drop checkers are good indicators if it's been long enough. I read mine at the beginning and end of the photoperiod, and they are always the same because I usually start my CO2 4-5 hours before lights on for a tank this big. They are a reliable indicator when used properly, but not precise.

I somewhat agree on ph/kh when used by most test kits/hobbyists. I'm using a laboratory pH meter and accurate kH tests. I also run remineralized RO and do a lot of water changes so there is really nothing affecting pH (e.g. dissolved organic carbon) or acid-base reactions other than these two components. So I would argue that these estimates are quite accurate and also in line with my expectations and visual assessments. I got a massive outbreak of BBA when I installed my first reactor and was only getting 15ppm under the same lighting (switching from a previous vertical mixing style reactor which was producing 30 ppm).

I also have measured pH drop from degassed aquarium water (ran a bubbler on it until pH stabilized), and I need this larger reactor to get anywhere north of 0.8-0.9 ppm drop.

Maybe we can figure out what elements of design, flow, and surface agitation are limiting, such that better guidance on sizing could be provided.
Some contributions here suggest that flow rate doesn't matter much, and I would agree with that based on my own observations. I can basically close off the reactor or send all the filter flow through it, and I get very similar CO2 when it's running in overflow mode regardless of flow. The adjustable ones are probably the way to go, but with DIY builds you have to build a version, see if it produces enough CO2, and if not built another (and another if you still are not where you are).

Having made this same style reactor with clear PVC, the reducer fittings actually only allow the air pocket to reach ~1/3 way down the side of the reactor wall. The original calculations assumes the air pocket spans the full width of the pipe diameter.

Either way, right there with you man. I've built THREE of these and cannot seem to get the sizing right for my 60P. For me the 17.7 ratio was too much but it seems that most people with bigger tanks have needed larger ratios.

 

[xNitroPT]

Having made this same style reactor with clear PVC, the reducer fittings actually only allow the air pocket to reach ~1/3 way down the side of the reactor wall. The original calculations assumes the air pocket spans the full width of the pipe diameter.

Either way, right there with you man. I've built THREE of these and cannot seem to get the sizing right for my 60P. For me the 17.7 ratio was too much but it seems that most people with bigger tanks have needed larger ratios.

I'm trying to do the same for a 60p right now. Do you have a video/pic of yours only functioning at 1/3?

 

[ScaperHaynes]

I'm trying to do the same for a 60p right now. Do you have a video/pic of yours only functioning at 1/3?

Sure thing, see attached photos. The CO2 pocket is usually a tad larger, the CO2 had just turned off about 30 mins prior.

 

[JayP]

My experience so far with DIY reactors on tanks under 50g: My reactors are designed to be adjustable by rotating them. I'm getting the CO2 levels I want, but in order to do so I have them rotated to a level where they should gas the fish and my "bubble" rates are very high. My theory as to why; too high of flow rate through the smallish size reactor. On my 25g tank, I'm running a Biomaster 250 and on my 49g tank, a Biomaster 600. Even limiting the flow with inline valves, it's still moving through the reactors fairly fast, not enough to be noisy, but still fast. I'm working on new reactors with bypasses to slow the flow down. Hopefully, if my theory is correct, doing this will allow me to adjust the reactors where the math says they should be and I can turn the CO2 flow down.

 

[xNitroPT]

Sure thing, see attached photos. The CO2 pocket is usually a tad larger, the CO2 had just turned off about 30 mins prior.

Ok I see what you mean now; you can only get to 1/3 since your outlet sits right at the center. I think the only way solve it would be to drill two holes into a pvc cap yourself or get something like a well seal. What are the dimensions of your yugang? (diameter and length) Cabinet looks great btw, I think we have the exact same setup and cabinet haha

 

[hamfist]

My experience so far with DIY reactors on tanks under 50g: My reactors are designed to be adjustable by rotating them. I'm getting the CO2 levels I want, but in order to do so I have them rotated to a level where they should gas the fish and my "bubble" rates are very high. My theory as to why; too high of flow rate through the smallish size reactor. On my 25g tank, I'm running a Biomaster 250 and on my 49g tank, a Biomaster 600. Even limiting the flow with inline valves, it's still moving through the reactors fairly fast, not enough to be noisy, but still fast. I'm working on new reactors with bypasses to slow the flow down. Hopefully, if my theory is correct, doing this will allow me to adjust the reactors where the math says they should be and I can turn the CO2 flow down.

Absolutely, you almost cannot have "too slow" flow through one of these. But too fast a flow easily messes them up.

 

[xNitroPT]

Just my contribution to the discussion on this forum .......
I have recently put together one of these reactors.

50mm clear PVC pipe
plain PVC end caps
50mm PVC union coupling to enable the reactor to be split in half if ever needed.
brass bulkhead barbed 12mm hose connectors

All glued together with PVC cement. The bulkhead connectors are sealed internally with silicon washers.
CO2 is currently injected just upstream via an inline diffuser with the ceramic removed. However, I think I will be adding a new 4mm bulkhead connector to inject the CO2 directly into the reactor as I am experiencing quite a large remnant bubble of other gases at the end of the day. I forget who but someone else on here reported the same thing which was rectified by injecting directly into the reactor. I will report back to let everyone know if it has the same effect on mine too.

I run the reactor in "overflow" mode.

I have the outlet pipe offset quite a way from centre to enable me to adjust the surface area by simply twisting the reactor, which is easy to do as its all plugged into a flexible hose circuit. Its plugged into a bypass loop in one of my EHeim 2217 outputs. I was not aiming for huge CO2 levels so went for a minimum tank surface area to reactor surface area ratio of around 35. It can be adjusted way more, easily up to around 100 if need be if I want less CO2 absorbtion. Its a 150 gallon tank so the internal reactor length is 52.5cm.

Note - the bypass loop seemed essential as it was way too noisy without it, and also sucked the gas out bigtime with a whirlpool type effect inside the reactor.
I've been running it at maximum reactor surface area for a few days and just tested the tankwater CO2 levels at the end of the "CO2 day" with my brand new Hanna CO2 test kit (a fine bit of kit) and it comes out at 32.5 ppm, so I'm really happy with that. I'll do further testing and fine tuning in the coming days to perfect the CO2 timing cycled. Water is of course crystal clear !!
Heres some pics. PLus a rough and ready snap of the tank. You'll see that my work is not laboratory engineer standards of neatness etc, but it does all seem functional !........
View attachment 10819View attachment 10820
View attachment 10821View attachment 10822View attachment 10823

I see you’re using brass fittings. Has this caused an issue for any of your shrimp/fish? My understanding is brass is >60% copper and especially in low tds / more acidic water it will leech.

 

[ScaperHaynes]

Ok I see what you mean now; you can only get to 1/3 since your outlet sits right at the center. I think the only way solve it would be to drill two holes into a pvc cap yourself or get something like a well seal. What are the dimensions of your yugang? (diameter and length) Cabinet looks great btw, I think we have the exact same setup and cabinet haha

Current pipe length is 2” diam x 4” length. Note that the reducers add a little surface area to CO2 pocket on each side but that’s hard to calculate without CAD software like I use.

Haha, yes the Aquaforest 60P and cabinet special

 

[Laurie131]

I want to thank @Unexpected for introducing me to this new forum, but most importantly for him being the first ever to build the Horizontal CO2 Reactor. I feel honored that "Yugang Reactor" as he calls it (Yugang 鱼缸 means fish tank) is introduced in @Unexpected journal, but it would be a pity if that journal gets cluttered with too much reactor talk. So let me open a dedicated thread for discussions, questions and help on this Horizontal Reactor.

I have been experimenting for years with CO2, and at some time I took videos of my (modified) Aquamedic reactor to watch the bubbles in slow motion. To my surprise I found that the combined surface area of the bubbles was not very high for achieving a 1.5 pH drop in my 250 liter tank, and that CO2 absorbs so fast in water that the lifetime of bubbles is quite short. So .... we don't need to juggle bubbles at all, we can just create a very simple absorption interface between flowing water and a pocket of CO2 above it. The Horizontal reactor is surprisingly simple, and has some benefits that we won't find in diffusers or conventional Cerges / Griggs bubble reactors:

• Simple rules to find the correct dimensions for any tank, a small nano tank or a huge tank the size of a swimming pool.
• Very easy and cheap to build with plumbing materials. No fragile parts, low risk of leakage or malfunction.
• 100% CO2 absorption efficiency
• No need to experiment with vortices, venturis, diffusers, needles wheels, impellers / rotors, multi stage reactors - it is just a pipe with a gentle flow of water.
• No noise
• No mist in the tank
• No maintenance, and stable performance over time
• Virtually no reduction of flow from pump
• A purging valve is optional, as the reactor will purge itself from excessive trapped air.
• The reactor can be configured so that in the event of a failure, CO2 injection will not exceed a limit and fish cannot be gassed. Inherently safe.
• The reactor can be configured so that we do not need a precision regulator, because the reactor controls the CO2 injection rate

View attachment 2030

Or a multi stage version ...
View attachment 2031

A detailed thread can be found on UKAPS, linked with the kind permission from Scapecrunch forum moderators #1

I am happy to help new users to verify the calculations on reactor dimensions for their tank, please send me a PM.

I’m somewhat new to the group and I’m not sure how to send a message. I’d like to know the size of reactor for my set up and maybe a recommendation for a video or site with specify build instructions.

My aquarium is a 75 g long (ish) and the dimension are 48 x 18 x 20. I’m running co2 and I think a reactor would help my set up because of the size - improve co2 availability in all areas. I’m currently running one fx2 - outflow positioned in the front corner, intake in the opposite back corner and the largest green machine uv sterilizer in the 4th corner just opposite the outflow. Theres also an air stone about six inches from the intake. I think circulation is adequate.
I really appreciate any advice you can give. Your information is super helpful and I really appreciate your offer to help figure this stuff out, because I recently watched an expert aquascaper install a reactor and the size was too much for his specific aquarium. I guess it’s easy to get the size wrong, so here I am.
Thank you.

 

[xNitroPT]

I’m somewhat new to the group and I’m not sure how to send a message. I’d like to know the size of reactor for my set up and maybe a recommendation for a video or site with specify build instructions.

My aquarium is a 75 g long (ish) and the dimension are 48 x 18 x 20. I’m running co2 and I think a reactor would help my set up because of the size - improve co2 availability in all areas. I’m currently running one fx2 - outflow positioned in the front corner, intake in the opposite back corner and the largest green machine uv sterilizer in the 4th corner just opposite the outflow. Theres also an air stone about six inches from the intake. I think circulation is adequate.
I really appreciate any advice you can give. Your information is super helpful and I really appreciate your offer to help figure this stuff out, because I recently watched an expert aquascaper install a reactor and the size was too much for his specific aquarium. I guess it’s easy to get the size wrong, so here I am.
Thank you.

Article 'Yugang CO2 Reactor - A Guide'

Contents: Benefits of Yugang reactor Calculate the reactor dimensions Overflow mode, regulator mode, pH/CO2 controller Overflow mode, step by step instruction Regulator mode, pH/CO2 controller mode, step by...

• Yugang
• Sep 15, 2025
• 20 min read
• Reaction score: 10
• Comments: 10
• Category: CO2 in the Planted Aquarium

If you have a 75gallon, assuming your 48x18x20 is L x W x H, your tank surface area is 48x18 which is 864. Depending on what pH drop you want, let's say 1.5, you would divide that by 17.7 (read the guide and yugang gives the numbers you should divide by to get the pH drop you want).

864/17.7 = 48.8

This will be what diameter and length of your yugang reactor needs to multiply to be.
Ex) 4 inch diameter and 12 inch length tube (4 x 8 =48)
Ex) 2 inch dimaeter and 24 inch length tube (2 x 12 = 48)
Both close enough to 48.

 

[Pepere]

I recall, not too long ago, reading on the forums where there were the amount of division you needed to calculate surface area of reactor for different co2 target levels. Ie divide tank aurface area by 17.7 to get surface area of reactor for 30 ppm etc. looking to get an idea of reactor sizing for different co2 ppm levels. Say 25 ppm, 20 ppm, 15 ppm etc…

Dies anyone else remember seeing this? Am I suffereing froma delusion or false memory?

 

[Pepere]

Duplicated post

 

[JayP]

I recall, not too long ago, reading on the forums where there were the amount of division you needed to calculate surface area of reactor for different co2 target levels. Ie divide tank aurface area by 17.7 to get surface area of reactor for 30 ppm etc. looking to get an idea of reactor sizing for different co2 ppm levels. Say 25 ppm, 20 ppm, 15 ppm etc…

Dies anyone else remember seeing this? Am I suffereing froma delusion or false memory?

I don't recall seeing calculations for specific PPMs but in the Yugang Guide in the Articles section, there are calculations for the specific PH drops.

Calculate the reactor dimensions

Summary:

• Calculate the Tank_Surface_Area (tank length * width)
• The target Reactor_Surface_Area between water and the gas pocket in the reactor (reactor length * reactor width) is proportional to the Tank_Surface_Area (for any given pH drop target).
• For a pH drop target 1.5, the Reactor_Surface_Area is estimated at Tank_Surface_Area / 17.7
• For a pH drop target 1.2, the Reactor_Surface_Area is estimated at Tank_Surface_Area / 35.4
• For a pH drop target 0.9, the Reactor_Surface_Area is estimated at Tank_Surface_Area / 70.8

 

[Mr.Shenanagins]

@Naturescapes_Rocco recommends dividing by 15 to get closer to 40ppm but he can explain the math it’s not my forte lol I’m basing my next build off of that standard.

 

[Pepere]

Thank you @techman81 That is what I was looking for. I just wasnt remembering it correctly.

 

[hamfist]

I see you’re using brass fittings. Has this caused an issue for any of your shrimp/fish? My understanding is brass is >60% copper and especially in low tds / more acidic water it will leech.

I have not seen any adverse affects at all, and I do have low KH, low pH water. There are a few amanos living happily in the tank too.

Its a 150g tank with weekly 50% water changes though, so dissolved metals from the connectors must be minimal. You have got be thinking about changing them for nylon ones though.

 

[SmartAlec13]

I don't recall seeing calculations for specific PPMs but in the Yugang Guide in the Articles section, there are calculations for the specific PH drops.

Calculate the reactor dimensions

Summary:

• Calculate the Tank_Surface_Area (tank length * width)
• The target Reactor_Surface_Area between water and the gas pocket in the reactor (reactor length * reactor width) is proportional to the Tank_Surface_Area (for any given pH drop target).
• For a pH drop target 1.5, the Reactor_Surface_Area is estimated at Tank_Surface_Area / 17.7
• For a pH drop target 1.2, the Reactor_Surface_Area is estimated at Tank_Surface_Area / 35.4
• For a pH drop target 0.9, the Reactor_Surface_Area is estimated at Tank_Surface_Area / 70.8

Sorry, new as well, just checking my math here...

My tank is a 60p, so 60x30x36cm. So my surface area would be, in inches, 24x12" = 288. So then my Reactor Surface Area would be about 16 for the 1.5ph drop, or 8 for the 1.2ph drop.

It just seems quite small, to do potentially an 8" long 2" diameter tube. Would my filter's flow (biomaster 250, set to like 50% flow power) be too much?

 

[xNitroPT]

I have not seen any adverse affects at all, and I do have low KH, low pH water. There are a few amanos living happily in the tank too.

Its a 150g tank with weekly 50% water changes though, so dissolved metals from the connectors must be minimal. You have got be thinking about changing them for nylon ones though.

Yea I'm opting to have stainless steel or nylon fittings right now on my setup. I'll be making some a post about a prebuilt option, instead of PVC, that I have for the yugang reactor that I think will be nice for people with smaller tanks (once I try it out).

@Yugang has been so generous and helpful to me, held my hand through the calculations and parts questions, and opened to for to the world is CO2 reactors. I wanted to say thank you and that I appreciate your help.

Here's what we came up with. This is for a 60U (24" x 14") 20 gallon tank. 2" clear schedule 40 conduit 6" in length. At first, I mounted the reactor above the canister filter with both 90° elbows pointed down like so.View attachment 5115
This worked ok, but ( I'll add that I built another reactor for my smaller tank) the other reactor has a slightly different design due to space limitations and it worked better. Both of those 90° elbows faced up. So I moved the reactor down and turned both elbows upward like soView attachment 5116
The flow is more gentle and less bubbles. I control the CO2 flow with a regulator. I did not install a bypass or overflow. I'm using double tap disconnects for maintenance and flow adjustment purposes. I'm running an Oase 350 on this tank and need to throttle it down a bit anyways. This quiets everything down and stops the gurgling and sucking in air at the skimmer. I easily hit 1 ph drop in 40 minutes. I'm using a John Guest fitting for CO2 connection, which is threaded into reactor body using 1/8 x 27 NPT tap and 21/64 drill bit.

Such a huge improvement over the inline diffuser I was using. No more micro bubbles!

Here' s an example of what you're asking about. This person has a biomaster 350. I have a 350 as well but it's way too strong in my yugang, it pushes water out like a tsunami so I feel like it's almost a must to have a bypass for smaller yugang reactors depending on the pump you're using. I had to close my tap valve to 80% for there to be "relatively" smooth flow in the reactor which slowed the water coming out of the outlet to barely any flow which I don't want. My reactor will be 40mm x 190mm for my ada60p.

 

[TRyan]

Yea I'm opting to have stainless steel or nylon fittings right now on my setup. I'll be making some a post about a prebuilt option, instead of PVC, that I have for the yugang reactor that I think will be nice for people with smaller tanks (once I try it out).


Here' s an example of what you're asking about. This person has a biomaster 350. I have a 350 as well but it's way too strong in my yugang, it pushes water out like a tsunami so I feel like it's almost a must to have a bypass for smaller yugang reactors depending on the pump you're using. I had to close my tap valve to 80% for there to be "relatively" smooth flow in the reactor which slowed the water coming out of the outlet to barely any flow which I don't want. My reactor will be 40mm x 190mm for my ada60p.

Do you use double tap quick connect valves to lower flow? I find them to be a must have item and use them on both of my Oase biomaster filters. They are also very useful for maintenance.

 

[xNitroPT]

Do you use double tap quick connect valves to lower flow? I find them to be a must have item and use them on both of my Oase biomaster filters. They are also very useful for maintenance.
View attachment 15453

Yea thats what I use to lower the flow. Any valve will work but this just helps with maintenance too.