CO2/pH controller recommendations?

[Clare]

Hello Everyone,

I'm struggling with my set-up at the moment. (It's a long story, including some stupid mistakes!)

I think things are on the improve, but I really need to sort out my CO2 levels. I've been using a drop checker (which I hate!) for my CO2 (and a cerges style CO2 reactor) and feel that I really have no idea what my CO2 ppm is in the tank. My plants aren't thriving, and algae is, so I'd really like to optimise my CO2.

I'm keen on getting a pH (CO2) controller but am going round and around in circles trying to work out what to get.

Any recommendations will be very gratefully welcomed!

 

[marekm]

I would suggest to consider a simple PH probe instead of a controller, which is cheaper. I dont use the controller feature, I am just using it to monitor the PH. The way the controller works is not ideal, since you would have CO2 fluctuations during the on/off stages, it is better to dial in CO2 using just the needle valve.
It might be useful if you want to prevent accidents, but a good 2-stage co2 regulator should be sufficient for this.

Regarding the specific model I cant make a suggestion, I am using a cheap probe with my controller and it is surprisingly accurate, last time I have calibrated it, it was spot on and didnt need any adjustments.

 

[Naturescapes_Rocco]

I'd also recommend checking out the Hanna CO2 titration test kit, which I've been testing for accuracy. They've helped me immensely in combination with drop checkers!

pH controllers are really not great for controlling pH over time. So many issues. Your KH changes and swings weekly, even in small amounts, after a water change. So does your pH, due to the release of acids and organic compounds over time.

I use a GHL Profilux 4 and GHL pH probe (all of the higher-end of the hobby) to track and control my pH, if I wish.

I'd just recommend investing in a good regulator with a precision needle valve, and use a combination of pH readings from a good pH pen in conjunction with Hanna CO2 test kit and drop checkers. Once you have a system dialed in like that, it's foolproof and avoids all the headache that comes from trying to control CO2 via pH. But that's just my opinion!

 

[Koan]

and a cerges style CO2 reactor

Since you are already using an external reactor, a correctly sized and set up homemade Yugang reactor will both improve your efficiency and stabilize your CO2, removing the need for a pH controller.

Or as Rocco says, a regulator with a good solid needle valve that won't drift will allow you to set the level you want and maintain it

feel that I really have no idea what my CO2 ppm is

The Hanna CO2 test is super easy to use and will tell you exactly how much you have at any given point

Resource Thread 'Hanna CO2 Test Kit: My experience so far (and why you're probably not starting CO2 injection early enough)!'

Mar 27, 2025

The 2hrAquarist legend Dennis Wong tested the Hanna Test Kit vs a $3,000+ CO2 testing device and found accurate results in low kH aquasoil based tanks when compared. $30 for CO2 readings vs $3,000+!

It's a simple kit that comes with simple instructions, two differently sized vials for different detection ranges, a titration syringe phenolphthalein indicator, and an NaOH solution of some unknown concentration to titrate with.

For the range of detection on the Hanna CO2 test kit we want (0-50ppm):

• Add 10mL of aquarium water to the small flask. Add 1...

• Naturescapes_Rocco

• 
• 

 

[GreggZ]

I may be in the minority, but I have been using a pH controller for many, many years and wouldn't be without it.

For me I like the set and forget aspect and the ability to fine tune very easily. Let's say my current pH low point is 4.95. If I want to see what 4.90 is like.....or 4.85.......I just dial it in and see what happens. It couldn't be easier.

Honestly I've read all about the Yugang reactor , and appreciate the innovation. But I have no desire at all to try one. The pH controller is just too easy to use and also acts as a failsafe for my rainbowfish.

One caveat is it only works really well for tanks where dKH is steady. I use pure RO so no issues there. If your dKH fluctuates a lot then a controller is not for you.

The model I use is the American Pinpoint Marine which is a rock solid unit. Mine is well over a decade old and works perfectly. The probe is a high quality double junction unit with a BNC connector. The probe keeps calibration extremely well and lasts a LONG time.

Now that being said I haven't bought a pH controller in a LONG time, and there may be more cost effective options out there. I just haven't looked into alternatives.

Now admittedly I am old school.........heck I still use T5HO! But once you've used a pH controller for a while you understand why they are so convenient. Like I said I wouldn't be without one. I have too much other stuff to worry about and try to fine tune, so I like that my ph drop from CO2 is a no brainer.

 

[JacksonL]

I use an Up Aqua ph controller, which was the only one stocked locally when I bought it many years ago.
I wouldn’t recommend it highly. It does the job, but is fiddly to set, has a wide gap (about 0.8 ph) between on and off cycles and the probe it comes with is poor.
I have upgraded to a double junction probe, which makes a huge difference. I still only use it as a backstop, in case my CO2 input is higher, or something happens (ie filter flow reduces, surface movement lowers, needle valve gets bumped), so it turns the gas off before my fish get gassed. It is nice peace of mind.
It is a ‘nice to have’, but if you are on a budget then I would put the money towards a flow meter and a reliable needle valve before the ph controller. The flow meter has been a game changer for me.

 

[GreggZ]

The flow meter has been a game changer for me.

I also use a flow meter. I set the flow just a bit higher than it needs to be then fine tune with the controller.

With a flow meter and controller the needle valve means little. In fact if I were starting all over I'd buy the cheapest single stage CO2 regulator with the cheapest needle valve and then use a flow meter and controller. Very dependable for me.

 

[Aquajack]

That's what I love about this forum, there are different perspectives, and many ways of achieving similar outcomes. I appreciate all perspectives, as it stops us all from travelling down the tunnel vision path.

Excuse my ignorance, but how do some of you use a flow meter? Is that to set an initial level, and monitor for stability and fine tune with the needle valve on the regulator? Or am I way off here?

 

[Clare]

That's what I love about this forum, there are different perspectives, and many ways of achieving similar outcomes. I appreciate all perspectives, as it stops us all from travelling down the tunnel vision path.

Excuse my ignorance, but how do some of you use a flow meter? Is that to set an initial level, and monitor for stability and fine tune with the needle valve on the regulator? Or am I way off here?

I was going to ask the same thing!

Have a CO2 art regulator with needle valve that I've used for a few years. Don't know anything about a flow regulator. (I have a 750ish L system, so don't bother with bubble counting)

 

[Clare]

I may be in the minority, but I have been using a pH controller for many, many years and wouldn't be without it.

For me I like the set and forget aspect and the ability to fine tune very easily. Let's say my current pH low point is 4.95. If I want to see what 4.90 is like.....or 4.85.......I just dial it in and see what happens. It couldn't be easier.

Honestly I've read all about the Yugang reactor, and appreciate the innovation. But I have no desire at all to try one. The pH controller is just too easy to use and also acts as a failsafe for my rainbowfish.

One caveat is it only works really well for tanks where dKH is steady. I use pure RO so no issues there. If your dKH fluctuates a lot then a controller is not for you.

The model I use is the American Pinpoint Marine which is a rock solid unit. Mine is well over a decade old and works perfectly. The probe is a high quality double junction unit with a BNC connector. The probe keeps calibration extremely well and last a LONG time.

Now that being said I haven't bought one in a LONG time, and there may be more cost effective options out there. I just haven't looked into alternatives.

Now admittedly I am old school.........heck I still use T5HO! But once you've used a pH controller for a while you understand why they are so convenient. Like I said I wouldn't be without one. I have too much other stuff to worry about and try to fine tune, so I like that my ph drop from CO2 is a no brainer.

Ha, yes I know what you mean re the yugang reactor . I really like the sound of it as it seems quite elegant, and hopefully will get around to it one day, but if I wait until I've put one of these together the entire tank will have been consumed by algae!

 

[Clare]

Also any words of caution re kH testing kits? Is there such a thing as a kH probe worth getting?

 

[TRyan]

I may be in the minority, but I have been using a pH controller for many, many years and wouldn't be without it.

For me I like the set and forget aspect and the ability to fine tune very easily. Let's say my current pH low point is 4.95. If I want to see what 4.90 is like.....or 4.85.......I just dial it in and see what happens. It couldn't be easier.

Honestly I've read all about the Yugang reactor, and appreciate the innovation. But I have no desire at all to try one. The pH controller is just too easy to use and also acts as a failsafe for my rainbowfish.

One caveat is it only works really well for tanks where dKH is steady. I use pure RO so no issues there. If your dKH fluctuates a lot then a controller is not for you.

The model I use is the American Pinpoint Marine which is a rock solid unit. Mine is well over a decade old and works perfectly. The probe is a high quality double junction unit with a BNC connector. The probe keeps calibration extremely well and last a LONG time.

Now that being said I haven't bought one in a LONG time, and there may be more cost effective options out there. I just haven't looked into alternatives.

Now admittedly I am old school.........heck I still use T5HO! But once you've used a pH controller for a while you understand why they are so convenient. Like I said I wouldn't be without one. I have too much other stuff to worry about and try to fine tune, so I like that my ph drop from CO2 is a no brainer.

I'm definitely ordering this ph controller. I've been using a homemade yugang reactor paired with a budget 2 stage regulator, ph probe and Dwyer flow meter for a couple years now. It's been working pretty well, but sometimes it drifts and I need to reset the dwyer. Not ideal.

Yesterday I checked ph level and it was down to 5.2. My normal 50 ppm CO2 level is about 5.55 ( degassed at 6.55) I checked the Dwyer flow meter and it was at 25 mark where it normally sits at 15. What happened? No clue, but I but know my yugang reactor is oversized and can still reach dangerous levels and things can go south unexpectedly.

This controller is a great idea and I'm going to give it a try.

Thanks for the info, @GreggZ

 

[marekm]

I may be in the minority, but I have been using a pH controller for many, many years and wouldn't be without it.

For me I like the set and forget aspect and the ability to fine tune very easily. Let's say my current pH low point is 4.95. If I want to see what 4.90 is like.....or 4.85.......I just dial it in and see what happens. It couldn't be easier.

Honestly I've read all about the Yugang reactor, and appreciate the innovation. But I have no desire at all to try one. The pH controller is just too easy to use and also acts as a failsafe for my rainbowfish.

One caveat is it only works really well for tanks where dKH is steady. I use pure RO so no issues there. If your dKH fluctuates a lot then a controller is not for you.

The model I use is the American Pinpoint Marine which is a rock solid unit. Mine is well over a decade old and works perfectly. The probe is a high quality double junction unit with a BNC connector. The probe keeps calibration extremely well and last a LONG time.

Now that being said I haven't bought one in a LONG time, and there may be more cost effective options out there. I just haven't looked into alternatives.

Now admittedly I am old school.........heck I still use T5HO! But once you've used a pH controller for a while you understand why they are so convenient. Like I said I wouldn't be without one. I have too much other stuff to worry about and try to fine tune, so I like that my ph drop from CO2 is a no brainer.

very interesting, 2 questions:

1. is there a way to know if my PH probe is single or double junction?

2. so the PH controller keeps switching CO2 solenoid on/off throughout the day? doesnt it cause:

• an increased wear on the solenoid valve
• unwanted fluctuations in CO2 levels?

 

[JacksonL]

That's what I love about this forum, there are different perspectives, and many ways of achieving similar outcomes. I appreciate all perspectives, as it stops us all from travelling down the tunnel vision path.

Excuse my ignorance, but how do some of you use a flow meter? Is that to set an initial level, and monitor for stability and fine tune with the needle valve on the regulator? Or am I way off here?

For me, it is both those.
I can fine tune, and it doesn’t matter if the needle valve jumps, just tune it down to the number I am chasing. No wondering if the minuscule turn made a difference, I can see on the meter exactly what my change in setting has done.
Then, I just check it whenever I open the cabinet to ensure it’s set right where it should be.
If the pH creeps down by a few points, then the controller jumps in and switches it off until it goes back to where it usually is. But day to day, the CO2 is consistent so it doesn’t come into play.
I can also see on the power meter I have it plugged into, if the controller had to do anything that day.

 

[JacksonL]

Here is a normal day, the variation is just the power meter averaging out across the day.


Here is a day when it came into play and turned off the solenoid.
Turned out I had a dirty pre-filter and wasn’t getting as much surface agitation from the filter. Cleaned and back to normal the next day.

 

[GreggZ]

That's what I love about this forum, there are different perspectives, and many ways of achieving similar outcomes. I appreciate all perspectives, as it stops us all from travelling down the tunnel vision path.

Excuse my ignorance, but how do some of you use a flow meter? Is that to set an initial level, and monitor for stability and fine tune with the needle valve on the regulator? Or am I way off here?

It depends on the flow meter. You can get them with and without a valve.

Back many years ago I saw how poor a bubble counter was for setting and controlling CO2 flow. There is no standard for bubble size, and when you get to a tank with any real size the flow is so high that it is more like a constant stream and way too difficult to count with any accuracy.

At the time I was aware of the Dwyer flow meters as they were used in a piece of equipment related to my work. So I added a RMA 150-SSV (SSV = stainless steel valve) flow meter to my set up. Keep in mind that the amount of flow we are measuring is VERY small in the scheme of things. So you need to have the right flow meter with the right scale. In our case we are measuring cubic centimeters per minute (cc/min).

At the time I didn't know of anyone using a flow meter and it seemed pretty radical. Over time that changed and now there are loads of people using them. The idea is that you can set the flow to a cc/min that works for your tank.

With the Dwyer's there is an RMA 150-SSV and RMA 151-SSV that are commonly used. The RMA 150 has a scale of 10-100 cc/min and the RMA 151 has a scale of 5-50 cc/min. In general the RMA 151 is good for tanks up to about 75G and the RMA 150 is good tanks 100G and over. There are also lots of other flow meters out there as well (i.e., Porter). You just need to be careful as again we are measuring cc/min. Some measure things like SCFH which stands for Standard Cubic Feet per Hour, which is WAY too large of a scale.

So the idea is that you set a flow rate of CO2. In my case I use the valve on the flow meter and mine is set to about 60 cc/min. So it makes fine tuning relative flow rates very easy, much better than a bubble counter, especially in tanks of any size.

I hope that helps. Let me know if you have any questions.

 

[GreggZ]

very interesting, 2 questions:

1. is there a way to know if my PH probe is single or double junction?

2. so the PH controller keeps switching CO2 solenoid on/off throughout the day? doesnt it cause:

• an increased wear on the solenoid valve
• unwanted fluctuations in CO2 levels?

In general there are two types of pH probes that people use. And like many things you get what you pay for. The cheapest are the pH pens. They require very frequent calibration as they drift very easily, and they often fail. Put it this way, you don't buy them you rent them, as they need to be replaced quite often.

Then you have higher quality BNC connected probes, both single and double junction. These are more stable and last much, much longer. With the double junction being the better of the two.

Now as to the pH controller this is how it works.

There is low and high set point. These set the "range". That is the level of fluctuation between the two. The middle of those numbers is the center value.

So let's look at my set up. My low set point is at 4.85 and my high set point is at 4.99. When the pH reaches 4.99 the solenoid is turned on and the valve is opened. The valve stays open until the pH hits the center point which is 4.92 then the solenoid turns the valve off. The pH can continue to drift down just a bit as there is still some CO2 in the reactor which takes a little way to dissipate.

I've never sat there and timed it but I would say it's at least 45 minutes or so between cycles.

So yes the solenoid does cycle on and off. The range determines how often that is. I can tell you that my solenoid is well over a decade old and works perfectly.

And there is some pH drift. But really it's a slight difference between very, very high and very high. In my case it's always between about 4.90 to 4.99. I don't think plants really care as long as there is ample CO2 in the system.

Now the thing I like the most is let's say I want to lower that just a bit. I can do so in accurate small increments and observe the plants and fish. And when I find a level that works well, I can keep it there with no thought at all.

And again acts as a failsafe for my Rainbows. If something happened with the flow or the regulator the solenoid turns the CO2 off which gives me piece of mind.

I hope that all makes sense and helps. Reach out with any other questions.

 

[Art]

I will chime in here as well.

Like @GreggZ, I've used a pH controller for years. I use it in the same way he does. However, mine is connected to the Neptune's Apex system.

The Apex has the benefit of alerting me to whatever I tell it. This was critical for me because I travel for work and am away from the aquarium often. Any deviation from my settings, it tells me. It can even take a desired action.

Here's an example. Let's say I set my bottom set point to 5 pH. If the system got stuck and continued to flow CO2 into the aquarium, the pH would drift down below that point. At 4.9 pH, the system would send me a text, an email and would send me a note via the app. If it reached 4.5 pH, the system would automatically turn off power to the solenoid and start air pumps to aerate the aquarium. It would then alert me that this happened.

Overkill to some but when you're a 1,000 miles away from your aquarium, it can literally be a life-saver.

 

[techman81]

In general there are two types of pH probes that people use. And like many things you get what you pay for. The cheapest are the pH pens. They require very frequent calibration as they drift very easily, and they often fail. Put it this way, you don't buy them you rent them, as they need to be replaced quite often.

Then you have higher quality BNC connected probes, both single and double junction. These are more stable and last much, much longer. With the double junction being the better of the two.

There are a lot of cheap poor quality PH "pens" out there, but I'm a big fan of the Apera PH60 which would be at the high end of "pen" type meters.
I've used it and a Milwaukee MW102 "BNC" style meter for years for both home brewing and now the aquariums. The Milwaukee is more than $100 more than the Apera and yet, I use the Apera far more often. It's simpler, more convenient, and I actually find that it drifts less than the Milwaukee. In fact, I've replaced the probe on the Milwaukee but never the Apera, although I did have an Apera fail on me years ago due to my own screw up. Just make sure to take good care of them and keep the probes in storage solution when not in use.

 

[GreggZ]

If it reached 4.5 pH, the system would automatically turn off power to the solenoid and start air pumps to aerate the aquarium.

Good point here. The controller can also turn on another piece of equipment like a bubbler. So if the low point is hit the bubbler is turned on.

I don't use mine that way but I could. I have very strong aeration that comes on fifteen minutes per hour to ensure high levels of O2 as well as CO2. Likely pretty much the same as if I had it connected to the controller, but I just control it with a smart power strip (KASA).