Yugang Reactor Inconsistency

[ScaperHaynes]

Hey all,

My DIY Yugang reactor seems to produce an inconsistent pH drop despite operating in "overflow" mode. Some days my drop checker is very green, and then there is a streak of days where it is quite yellow. I'd like to get this ironed out before I buy any fish so I don't gas them.

So far, I've explored the following causes for inconsistent day-to-day drops but none have consisently reproduced the issue.
1. Water Level & Surface Agitation --> Water level relative to filter outlet causes more or less surface agitation, and therefore different pH drops
2. Skimmer Operation --> whether or not filter inlet skimmer is operating properly that day
3. Bubble counter --> whether or not the bubble counter has run dry
4. Injection rate --> even in overflow mode, it can be tuned to purge more or less frequently depending on bubbles per second. In theory, this shouldn't change anything but seems to have at least some impact. I've done my best to completely purge the reactor of any air that gets trapped from water changes/filter cleaning so that it's pure CO2.

Anything I'm missing here that I should look at for potential causes?

After doing some more detailed math using CAD, my reactor is a little over-sized for this tank (approximately 1:20 reactor to tank surface area ratio). The reactor is 2" x 8" Clear Schedule 40 PVC pipe. While this explains why I sometimes get too large of a drop, it still doesn't explain why it's a bit inconsistent day to day.

@Naturescapes_Rocco @Yugang Would you all have any feedback on this?

 

[Koan]

Some days my drop checker is very green, and then there is a streak of days where it is quite yellow

For your sanity's sake I would really recommend picking up a Hanna CO2 test kit, and find out exactly what those ppm values are

Journal Post in thread 'Recovering from disaster: My 120P journey.'

Jan 3, 2026

Right now I'm thinking its inconsistency in the CO2 that I'm just not seeing

Using the Hanna CO2 kit, to directly measure CO2 instead of inferring from pH drop, can also remove this uncertainty for you

• Koan

• 

 

[ScaperHaynes]

For your sanity's sake I would really recommend picking up a Hanna CO2 test kit, and find out exactly what those values are

Journal Post in thread 'Recovering from disaster: My 120P journey.'

Jan 3, 2026

Right now I'm thinking its inconsistency in the CO2 that I'm just not seeing

Using the Hanna CO2 kit, to directly measure CO2 instead of inferring from pH drop, can also remove this uncertainty for you

• Koan

• 

I've got both an Apera pH60 and a Hannah CO2 kit, and I find the CO2 kit very difficult to read consistently. Trying to dial it in using both methods though.

 

[Pepere]

I found that with a spray bar, if I am overflowing too much co2 it tends to build up in the spray bar and in essence create a second horizontal reactor causing higher output.

 

[Naturescapes_Rocco]

What's your KH? Zero?

 

[ScaperHaynes]

What's your KH? Zero?

Ah, another thing I'd meant to put on my list of potential causes. KH is currentl 3 dKH .

 

[Naturescapes_Rocco]

An easy way to smooth things out is to start injecting much earlier. If your lights come on, try starting CO2 at 4 or 5am, or even earlier, to help get things dialed in. If your DC is still green after 5 hours of injection, your setup is not good.

 

[hamfist]

It sounds like a tricky one. Personally I am a great fan of the Hanna CO2 test kit but I find it's important to sample from the same place and depth in the tank each time for consistency. Ideally somewhere down where the plants are. Sampling and testing like this with the Hanna test produces rock solid and repeatable results from my 500 litre tank plus Yugang reactor .

You have mentioned all sorts of things that could potentially cause variation. My thoughts are that the biggest two potential ones are differences in flow around the tank between days. As you suggest, maybe this could be linked to water level or skimmer use. Its difficult to see much else that would make a significant difference.
However, the prime suspect for me would be differences in sampling point for testing, especially for use of the Hanna test. It all might point to potentially sub-optimal water flow within the tank, with significant CO2 level differences in different areas of the tank.

 

[BigWave]

Well you all should know my thoughts on this reactor by now. Im still truggling with it. Seems even with a calibrated Hanna CO2 test kit saying I have 45 ppm CO2, the tank and plants dont lie that there isnt enough. Just saying..... It speaks volumes when I add in that dosing 30mL Excel into 20 gallons makes the plants perk up.

 

[hamfist]

Well you all should know my thoughts on this reactor by now. Im still truggling with it. Seems even with a calibrated Hanna CO2 test kit saying I have 45 ppm CO2, the tank and plants dont lie that there isnt enough. Just saying..... It speaks volumes when I add in that dosing 30mL Excel into 20 gallons makes the plants perk up.

Seriously, thats such a shame, when its working so well for some.

 

[ScaperHaynes]

After a little digging, the main problem seems to be what counts as "overflow mode". If my reactor purges a little CO2 every 3-5 minutes, the resulting drop is a lot less consistent day to day than if my reactor purges every ~1 minute. Seems I might be operating in a zone that isn't quite overflow mode, but also not regulator mode.

What I've found the last few days is that if I start with an overly high bubble count and work my way down, that produces results more consistent with the reactor sizing math. But, it does seem to purge CO2 quite frequently even if not a ton at a time. This also leads me to wonder if I'm really saving CO2 with this method or not.

Can anyone chime in on what is "normal" here in terms of how often the reactor should purge in overflow mode?

 

[hamfist]

Mine purges about every 30-60 secs. My understanding is that if it doesn't purge enough then the build up of nitrogen and O2 in the reactor's bubble builds up, thus the % of CO2 in the bubble drops, thus tank CO2 levels will be less than if the reactor bubble is a really high % CO2.
Even purging so much, I find at least a 30-40% CO2 saving for the same tank CO2 levels compared to using an inline diffuser.

 

[ScaperHaynes]

Mine purges about every 30-60 secs. My understanding is that if it doesn't purge enough then the build up of nitrogen and O2 in the reactor's bubble builds up, thus the % of CO2 in the bubble drops, thus tank CO2 levels will be less than if the reactor bubble is a really high % CO2.
Even purging so much, I find at least a 30-40% CO2 saving for the same tank CO2 levels compared to using an inline diffuser.

Good to know! I thought it was supposed to be less frequent than that. This still makes me wonder if this method really saves CO2 over a traditional diffuser…

 

[hamfist]

This still makes me wonder if this method really saves CO2 over a traditional diffuser…

Well all I can report is that it does for me, and a fair few others have reported the same.

For those who think they do not find a saving in CO2, I do wonder whether they have actually been reaching the same tank CO2 levels pre-Yugang reactor as they are now achieving with the new kit. Setting up a Horizontal CO2 reactor is often combined with getting new methods of CO2 testing, so the "pre" and "post" CO2 levels may not be directly comparable.

 

[xNitroPT]

Thought I’d ask the question here since the main thread was about co2 reactor inconsistency. If you’re using a yugang reactor with a ph controller, what’s stopping the co2 from continuing to dissolve and lower ph even when the solenoid is shut off? Maybe this is my misunderstanding on the purpose of the yugang reactor and that you are supposed to fine tune it so that it consistently stays at 30ppm during the photoperiod.

 

[Mr.Shenanagins]

I’m no scientific expert, but my understanding is that just because the injection stops, diffusion doesn’t just halt since the bubble of gas is still present and will continue to diffuse with the flow of water. Granted, it will slow down since injection has ceased, but once the bubble begins to subside and co2 dissolves then the pH should steadily rise.

As you’ve indicated, the Yugang is meant to be used in overflow or fine tuned with a needle valve. YMMV, as I believe @Naturescapes_Rocco tuned his to inject quite a large amount several hours before lights on to get a consistent and stable CO2 ppm during peak light hours. I also think that having a setup slightly larger than surface area required by the math leaves less room for error or insufficient CO2.

 

[Koan]

using a yugang reactor with a ph controller

Well a Yugang reactor is engineered physically to replace the need for a pH controller the mathematics of your construction set you up with a maximum CO2 injection rate, above which it can't go.

That is primarily what @Yugang designed it for, that plus a bubble-free display tank

 

[xNitroPT]

So I ended up returning my pH controller and choosing to use a yugang reactor . Let's say I start a new tank and dial in the co2 that the plants need. As they grow and take up more co2, would I need to adjust the amount of co2 going in? Not sure if the plants will even take up that much co2 to stop the overflow from happening or if the overflow already accounts for this to begin with. If I do need to adjust co2 going in, how often should this be recommended to check on this?

 

[Count Krunk]

Following along, good thread already.

My understanding is the reactor delivers that amount of co2 based on reactor volume, not plant density. So, theoretically, regardless of plant uptake the co2 level in the water should stay the same, no?

 

[Naturescapes_Rocco]

For the most part, that's what I've seen (using both pH readings from my aquarium computer over time, and from Hanna test kits).

When you're dosing 40ppm CO2 at equilibrium, as soon as plants consume CO2 there is now more "room" for CO2 to be dissolved into the water, and it reaches equilibrium (40ppm) fairly quickly.

Where we see CO2 drops is in natural ponds and low tech soil scapes, where CO2 builds up overnight from bacterial/plant/fish respiration, then is consumed during the day.

In our high tech setups the amount of CO2 consumed is likely not a very big deal. Aim for 30-40ppm through the entire photo period and you're likely providing plenty of CO2.