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

[Naturescapes_Rocco]

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 drop phenolphthalein and swirl gently.
• With the titration syringe (markings are "reversed" from traditional syringes), add the NaOH solution dropwise and swirl gently until color goes from clear to pink. Don't shake/agitate, or you will de-gas your CO2 concentration.
• For the 50ppm detection range, multiply the number on the syringe by 50 to get your result (if you used 0.4mL NaOH to turn the vial pink, you would have 20ppm CO2).

My findings:​

It seems to be "accurate" based on my comparisons with 1) drop checkers, 2) my pH reading/meter, and 3) the inhabitant-response (fish gasping at 35+ppm, shrimp uncomfortable at 30ppm+). It's not perfectly accurate (±5ppm), but it does a good "instant" job at giving some information in about 1-2 minutes. The kit also comes with enough for MANY, many tests (at least a hundred). For $30 I think it should become standard equipment for most CO2-injecting hobbyists.

I was worried about interactions with other acids in the flask, and I'm sure there are a few, but in clean, low-kH water, it doesn't seem like a problem. I found some stuff online from published journal articles about how there are no other worrisome strong acids to compete with the NaOH and that the CO2 readings from NaOH titration are generally accepted as accurate (in peer-reviewed journals). Not a silver bullet for CO2 testing, but really helps me get an understanding of my tank and keep it dialed in.

How I use it​

• If I want a quick glance of CO2 concentration for whatever reason in that moment (e.g., my fish are lethargic or shimp are at the surface).
  
  OR, the more complex way using it to dial in CO:
  
  
• Day 1 of CO2 on a new tank: I keep an eye on inhabitants and their behaviors (to make sure I don't over-inject) and I test 2-3 times throughout the day. The most important is the test done right before the CO2 shuts off, which would be the maximum CO2 level for the day. As long as I didn't get to "true yellow" on my Drop Checker, I hopefully plateaued in terms of injection, finding the equilibrium between injection and off-gassing.
  
  
• On Day 2: CO2 comes on 1-3 hours before the photoperiod. I compare the CO2 readings at the very start of the photoperiod, once during, and once at the end. A quick estimative plot on the graph should tell me if I'm at/around equilibrium.
  • For example, if my tank tests 6-10ppm CO2 before the solenoid turns on, then 20ppm when the lights come on, then 25ppm halfway through the photoperiod, and 30ppm by the end of the photoperiod, I know I'm somewhere in the proper "zone" (highlighted in pale yellow):
    
    
    
• On Day 3: I double-check the measurement at the start of the photoperiod, during, and at the end of the CO2 injection. As long as all 3 are close/approaching 30ppm, we're good!

On general timing of CO2 injection in this hobby:​

I continue to hear/read from reputable sources about how plants use the most CO2-per-hour in the first 3-4 hours of the photoperiod, which is why it's so important to have CO2 injection reach/near 30ppm @ equilibrium between injection and off-gassing.

Many beginners inject too little, or start injecting too late relative to their photoperiod. As Wong states in his article here,

"This scenario can give rise to a situation where CO2 levels are very high by day's end, with fish gasping at the surface. Hobbyists are puzzled as to how fish can be gasping and yet their plants are not getting enough CO2. This is unfortunately an extremely common scenario in the planted tank world when people use low injection rates coupled with poor gaseous exchange."

I think many users fall in the "Low injection rate" category, where they are only hitting optimum CO2 levels in the afternoon (when plants are using less of it to begin with!):

But they don't realize that you can fix that either by 1) increasing surface agitation (for increased off-gassing) as well as increasing injection rate:

OR by 2) Starting your CO2 injection way earlier than you think. For example:

Many hobbyists read "turn CO2 on 1 hour before lights" and end up with this:

Where they are only reaching optimum levels waaaay too late in their photoperiod, when they really should either start the CO2 way earlier, or start their photoperiod way later, like this:

To bring it all home (what I think):​

• The Hanna CO2 test kit is a lot cheaper than a reliable pH pen/meter/computer, and requires no calibration fluids or calibration itself.
• It's been tested to be somewhat accurate when compared to a very expensive aquatic CO2 testing device.
• You can use something like the Hanna CO2 test kit to test for whether you're starting CO2 early enough, or whether you are even reaching equilibrium between off-gassing and injecting CO2.
• Like all titration, it can be prone to user error. If the goal is light pink, everyone will see light pink differently. Just do your best to be consistent with your readings!
• It costs $33+ shipping and will likely last the average user a few years (if the reagents don't go bad before then). Worth it!

Just another tool in the toolbox to help us with our tanks. Let me know what you think!

 

[HarryL]

Is it just me having trouble accessing the attachment 7500? Says "The requested page could not be found."

 

[Naturescapes_Rocco]

Is it just me having trouble accessing the attachment 7500? Says "The requested page could not be found."

Try reloading, I should have fixed it!

The graphic is my image here:


It shows that even though I inject CO2 starting at 5am, I don't have the lights come on until 10am so the water is fully saturated with CO2 at 30ppm at equilibrium between injection and off-gassing. I turn CO2 off about 2 hours before the lights go off, since the plants are using less CO2 at that point anyway, and it takes a while for the off-gassing to occur to any meaningful amount.

 

[HarryL]

So did you intentionally have CO2 on for 5 hrs at lower bps because you have lower surface agitation? Or what is the reason you don’t opt for it to reach 30ppm 1-2 hrs before lights are on?

 

[Naturescapes_Rocco]

Great question, shows you know what this is all about!

(I sort of answer it in this thread: Testing the Aqua Rocks Colorado Acrylic Horizontal CO2 Reactor on a large tank)

Basically, the problem with horizontal reactors is that the injection rate is tied to the injection maximum amount of CO2.

If I run my reactor on max power (50% full of CO2), my injection rate is really fast (1.5 hours to reach ~30ppm) but it continues to inject, and the maximum CO2 injeciton/offgassing equilibrium is close to 50ppm (too much for my fish). The two options I have are to either 1) reduce the max power of my reactor (which also reduces the injection rate), or 2) agitate the surface more to "flatten" the curve through off-gassing, like this (line A):


I can't really agitate the surface much more than I already am -- I already have two filters with outlets at the surface, creating ripples across the entire surface of the tank. I suppose I could add a cooling fan to hit the surface, or add a wavemaker pointed at the surface, but then I might have too much current for my liking.

The simple option for me was to run my reactor at only ~1/3rd full, and just start my injection way earlier in the day! I still get the curve-flattening from off gassing eventually (line B in the above graph), but I don't need to worry about gassing out my fish because the reactor really caps right at the proper 30ppm CO2.

So, I end up with this:

And all is well!

I really wish this was better explained in the hobby. Credit to Dennis Wong for making it more widespread and approachable.

 

[HarryL]

I did a majority of my learning from Dennis’ website as well, so many useful information, I pretty much read every article he has.

I never really thought about measuring the concentration after the lights are on. I use a diffuser and when I first started injecting, I measure the pH just like how Dennis suggested. If I get a 0.8-1.0 pH drop from a completely off-gassed sample, then I let it stay that way without any further adjustments. I actually forgot to run the light on schedule once, it stayed off while CO2 remained on for the whole day, all shrimp and fish seem perfectly fine when I came home. I wonder if the small amount of light from the window enabled enough photosynthesis to help offset the CO2 level, or the CO2 just happened to be plateauing with whatever off-gassing rate the tank has.

With one of my tanks I currently do different light intensity during different time of the day to control algae. Since the plants use the most CO2 in the first few hours, do you think it makes the most sense to start with higher intensity as well, then lower the intensity?

 

[Naturescapes_Rocco]

Since the plants use the most CO2 in the first few hours, do you think it makes the most sense to start with higher intensity as well, then lower the intensity?

I think this is a great topic worth experimenting with! In relation to CO2 use, it makes sense, however, what if plants uptake CO2, but actually perform the majority of their photosynthesis in the afternoon? Is that why we see more oxygen bubbles in the midday/evening, even though plants uptake more CO2 in the first part of the photoperiod?

It would be fun to set up two identical tanks, and try this very idea. Who knows, maybe it is actually more beneficial to have stronger light in the second half of the photoperiod for some reason! If anyone else knows I'd love to hear.

 

[Burr740]

Great thread

 

[Koan]

The Hanna CO2 test kit is a lot cheaper than a reliable pH pen/meter/computer

And word is getting out! Hanna has it on back order they don't expect any more to ship for at least 3 weeks

 

[Naturescapes_Rocco]

Here's the Hanna CO2 test kit instructions (two pages)!

One thing I've been thinking about: my readings may be super accurate because I use a reactor, so the CO2 is 100% dissolved into my water. Could this kit be as accurate for tanks using a diffuser? Most likely, but might be something to note.

 

[BenB]

And word is getting out! Hanna has it on back order they don't expect any more to ship for at least 3 weeks

For anyone who is really interested to try this, LaMotte makes a kit that operates the same. It is more expensive though. LINK
I have this one, but I bought it decades ago before there was a Hanna, as far as I know. My reagents have long since expired.

 

[BenB]

I was worried about interactions with other acids in the flask, and I'm sure there are a few, but in clean, low-kH water, it doesn't seem like a problem. I found some stuff online from published journal articles about how there are no other worrisome strong acids to compete with the NaOH and that the CO2 readings from NaOH titration are generally accepted as accurate (in peer-reviewed journals). Not a silver bullet for CO2 testing, but really helps me get an understanding of my tank and keep it dialed in.

First: This is an excellent thread. It's a lot to take in, but it all makes good sense. It just takes some brain absorption time.

Second: This statement made me curious. (bold above) Maybe I am not understanding it, but many of us used the ph/KH table for 10-15 years before drop checkers were invented and grew great plants. Granted the number of species in the hobby has maybe tripled since then, but now we are told the pH/KH table is unreliable and shouldn't be used, again even though it worked for years, because other substances in the water could be affecting pH.

I wouldn't be surprised if someone has done direct CO2 measurement and compared to the pH/KH table, and I'm just not aware, but I'd be curious for you to do that next time you are running some CO2 tests on your tank. As you say above, it might not be "perfectly accurate," but surely close enough to not warrant the demonization it has received from so many in the last decade. (I hope I didn't miss somewhere that you addressed this)

 

[Yugang]

As you say above, it might not be "perfectly accurate," but surely close enough to not warrant the demonization it has received from so many in the last decade.

The pH/KH/CO2 table has limitations, both practical and theoretical. Its origins date back to the early days of CO2 injection, and there was no solid theoretical basis or accurate verification for it at the time. However, over the past decades it has been verified against tests with pH probes and professional CO2 meters, and it appears to work well in most cases.

Despite its limitations, the pH/KH/CO2 table remains a useful tool for hobbyists, though professionals and scientists may have reservations about its accuracy.

CO2 Chart

 

[BenB]

You've made me curious. I should be able to test my CO2 soon.
Your charts and write up have me thinking. Like many people, my light comes on and ramps up.
Do I want my CO2 at 30ppm when the lights come on, or by the time they reach full power.
I'm not sure I want it to hit 30ppm too early. Might get too high before the plants have enough light to start photosynthesizing and pulling it out.

 

[Naturescapes_Rocco]

You've made me curious. I should be able to test my CO2 soon.
Your charts and write up have me thinking. Like many people, my light comes on and ramps up.
Do I want my CO2 at 30ppm when the lights come on, or by the time they reach full power.

It's fairly well documented that plants take up the majority of whatever CO2 they're going to take up for the day in the first half of the photoperiod. Towards the afternoon, the rate of CO2 use drops dramatically.

Yes, if you want to maximize CO2 efficiency, I would suggest having the CO2 concentration already at max/equilibrium at (or around) when your lights come on. Better to have it at max for the first half, than only reaching max later in the photoperiod.

I'm not sure I want it to hit 30ppm too early. Might get too high before the plants have enough light to start photosynthesizing and pulling it out

What is "too early"? Most natural CO2-enriched waters (ponds with decomposing material, underground-spring-fed rivers in Brazil) have their CO2 levels rise quickly overnight, and drop during the day due to plant and algae activity.

Don't forget that you absolutely can run CO2 24/7 in your tanks -- it's just a waste to do so.

At Aquashow in Poland, they run some of their tanks 24/7 with CO2 because CO2 is super cheap, and they believe it's better for the plants to have access to carbon all the time rather than just some of the time.

Skip to 4:40 of this awesome video to hear it yourself:



I used to start my CO2 only 1 hour before the photoperiod, and "ramp up" my lights gradually, and I had different rates of success and struggled to grow some plants.

I've since switched to my CO2 starting much earlier, reaching a tested equilibrium (between injection and offgassing) in all my tanks before the photoperiod comes on. This is usually between 2-5 hours depending on the tank, method of injection, and surface agitation. The difference is insane--by midday, my plants pearl so much they turn the tank into sprite water. The CO2 turns off 1-3 hours before the lights go off. Beautiful growth rates.

I really believe that in a few years time, this will become the commonplace standard for timing CO2 injection, and we'll look back on the way many/most injected CO2 as "way, way too late in the photoperiod"!

 

[BenB]

Yes, if you want to maximize CO2 efficiency, I would suggest having the CO2 concentration already at max/equilibrium at (or around) when your lights come on. Better to have it at max for the first half, than only reaching max later in the photoperiod.

What is "too early"? Most natural CO2-enriched waters (ponds with decomposing material, underground-spring-fed rivers in Brazil) have their CO2 levels rise quickly overnight, and drop during the day due to plant and algae activity.

Well, that's kind of my question. When the lights come on, they aren't bright enough for the plants to photosynthesize yet. So do I want it at 30ppm then or 30 minutes later when they are at full strength?

I don't really feel like what happens in a pond or river is always applicable to my little tank. I don't have livestock yet, but any animals in those conditions will have adjusted to it.

Don't forget that you absolutely can run CO2 24/7 in your tanks -- it's just a waste to do so.

Yeah, I did that years ago, but it wasn't worth the worry and loss of CO2.

I've since switched to my CO2 starting much earlier, reaching a tested equilibrium (between injection and offgassing) in all my tanks before the photoperiod comes on. This is usually between 2-5 hours depending on the tank, method of injection, and surface agitation. The difference is insane--by midday, my plants pearl so much they turn the tank into sprite water. The CO2 turns off 1-3 hours before the lights go off. Beautiful growth rates.

I really believe that in a few years time, this will become the commonplace standard for timing CO2 injection, and we'll look back on the way many/most injected CO2 as "way, way too late in the photoperiod"!

OK. This was kind of what I was shooting for. I'll play around with it with a goal of 30ppm when the light is at full strength and then switch to 30ppm when it first comes on and see if I can see a difference.

The refill reagents for my CO2 test kit should be here tomorrow, but the tank comes on usually when I'm at work. So there are limited days when I'm home when the lights come on. It might talk a few weeks to test, adjust, observe, and repeat.

Thanks for the info.

 

[Kwyet]

Don’t you risk killing your fish if you leave it at max 24/7, because the plants are putting out CO2 at night instead of taking it up? I keep my little shrimp tank going 24/7, but it only has 10 ppm CO2. I would be worried doing that at 30 ppm unless there’s an airstone or something going at night too.

 

[Naturescapes_Rocco]

Don’t you risk killing your fish if you leave it at max 24/7, because the plants are putting out CO2 at night instead of taking it up? I keep my little shrimp tank going 24/7, but it only has 10 ppm CO2. I would be worried doing that at 30 ppm unless there’s an airstone or something going at night too.

This depends on your dissolved oxygen! CO2 and Oxygen are independent in water.

If you have little to no surface agitation (or a tall skinny tank), constant 30ppm of CO2 might be intolerable for some/most species of fish.

However, if you have a regular-shaped tank with good surface agitation constantly introducing fresh oxygen, you can easily increase the level of CO2 injection into a tank, 24/7 or not. Dennis Wong has a great article on this: Surface agitation & gaseous exchange in CO2 injected tanks.

You could have a tank at 30ppm CO2, 24/7, as long as you also have enough oxygen and flow in the tank. Sure, plant respiration might increase the ppm of CO2 in the evening by 5 to 7ppm, but it might not even be that much. As long as you have enough oxygen in your water, you could have CO2 at 40ppm.

My tank sits at about 30ppm when the lights come on, then at 35-40ppm for the next 8 hours. I'm pretty confident I could run the CO2 at 35ppm 24/7 and not stress any fish, because I have serious surface agitation oxygenating my water.

I want to reiterate! I'm not saying you should leave your CO2 on 24/7 like they do at Aquashow. I'm just saying that it's worth it to "waste" an extra hour of two to inject your CO2 to levels that are close to your target by the time the lights come on, and throughout most of the photoperiod.

It would be WAY better for your tank to have 20ppm CO2 24/7 with good oxygenation and agitation, than to have a constant swing from 5ppm to 35ppm every day too late in the photoperiod (this is what so, so many hobbyists do I believe).

 

[BenB]

Received my refill reagents for my test kit today.
Didn't anticipate that the syringe might be stuck after 20+ years of disuse. The plunger popped out of the rubber end. I eventually got it going though.
It was really hard to tell when the test was done. As @Naturescapes_Rocco said, it is a very faint pink. I'm going to try again tomorrow. I'm too dead tonight to fool with it.

 

[BenB]

Got a chance to piddle with my test today and read it in good light
CO2 was 25, 30 minutes after the CO2 came on.
CO2 was 30, 30 minutes later when the lights came on and started their ramp up
CO2 was 39, 30 minutes later or 90 min after the CO2 came on when the light were at full power.

Might be a bit of error since it went every 30 minutes from 25 to 30 to 39. It is a bit tricky to read and the drops aren't super accurate.

I wanted to test an hour later, but I had things to do. I don't have any livestock, so no idea if the levels were too much, but with the lights at full power, I would think use of the CO2 would be maximal. I probably need to dial it back just a bit. I also have a UV filter with a powerful power head churning the water. The CO2 is running too fast for when that power head isn't in there. I want to test more, but I can't seem to get out of the green water/greed dust algae cycle. I'll figure it out eventually.