oxyguard CO2 meter

[yme]

as one might know, I have an oxyguard CO2 meter. The last couple of months I set the pH value so that I would get a CO2 level of 37 mg/l. tank does not look oke, stunting etc. just the usual stuff.

Because I have this CO2 meter I didn't calibrate my pH probe for more than a year. Last week I did recalibrate the probe. As one might expect, it was a bit off. I was curious how this would affect the CO2 level, so I didn't change the settings of the pH computer. After 2 hours I measured the CO2 level of the tank. It was 65 mg/l! fish and shrimps didn't behave differently. What does this mean?? 65 mg/l CO2 and no stress? Is that possible? I recalibrated the CO2 meter again, but this didn't change the reading significantly.
Could it be that the CO2 meter gives false readings? How could I test this? Are there solutions with a known amount of CO2?

If the readings are correct, could 37 mg/l result in a C-deficiency? I do have the impression that I see more pearling.... (and since I have stunting rotala...)

greets,

yme

 

[Gerryd]

Hi yme,

I assume you use the ph probe to control the ph set level for the c02?

If so, could it be that you ORIGINALLY assumed that a target of 40 mg/l was 'sufficient' and never really went over that level thinking that it was simple overkill and not necessary?

Then with that number in mind all of your subsequent thinking was colored by it?

Remember that 40 ppm of c02 is a recommendation only. So few folks have taken any real measurements that have been published using a c02 meter that I doubt if anyone knows yet what a 'average' level might be.

The fact that your fish and critters are unaffected but the pearling seems more intense (is it or not?) tells me that your target of 37 mg/l was too low FOR YOUR TANK.

If I remember you have a decent sized tank and lots of bio-mass. This could demand a higher level of c02 than we might think.

I would continue to slowly increase c02 and see if the stunting goes away over time. Just a little once a week and watch your fish and shrimps for signs of stress and back off is so.

I have found that adding more surface ripple allowed me to INCREASE c02 (over time) where the fish had been stressed at a lower level of c02 WITHOUT the increase surface ripple.

Either way I hope that your days of stunting will soon be over.

Please keep us posted.

I hope some of this helped?????

 

[Tom Barr]

Pure water at equilibrium should have a CO2 of about 0.5ppm.
This is at the low end of the slope however.

I measured 60ppm at the 30cm distance from my outflow that had a venturi mazzei CO2 in line.

In the plant beds, the CO2 was only 15ppm.
At the immediate outflow, the CO2 was 80-100ppm.

Most pH/Kh readings error to show a higher CO2 ppm that is really there. This is due to added buffers that influence KH and also due to acids that reduce pH more than pure water.

Unfortunately, the tank's water is not pure.
So we add some fudge factor into the reading, it can be way off by using those methods(pH/KH).

The CO2 is suppose to help and it's certainly closer to the true measure.
Still, you never know unless you calibrate against a set of known standard CO2 ppm solutions.

For us, a 5, 30, and 50ppm would be good.

I'm not aware of anyone that sells them.
Adding the probe to these without losing any CO2 to degassing to the air would/is tough.

They do sell CO2 gas reference ppm's, but not dissolved.
I suppose you could make your own from those.

Still, without using calibration references, the CO2 oxyguard probe may or might not be off. I think it's far more reliable than the pH/KH, and more consistent.
However, over time, I have to wonder.

I'd like a reference for 30ppm personally. The CO2 is set at 40-45ppm for the larger client's tank and has been that way for over a year now with no plant issues, the light is pretty low however(150 to 25micromol depending on depth and position over 1.25 meters)

We got sort of testy with Oxyguard over the probe and sent it back for recalibration. I'm still not comfortable not knowing for certain with a reference in the range of interest(20-40ppm).
The solution is not an easy one.

CO2 is a bear to measure precisely and accurately.



Regards,
Tom Barr

 

[yme]

hi gerryD,

I don't know whether your answer is helping .
pearling looks to me more intense, but yeah, that is just an observation....

It would be nice if there were solutions with a known amount of CO2, to test whether the CO2 measurement is accurate. Anyway, the manual states that the measurement range is 0-50 mg/l. So the 65 mg/l might be somewhat off as well.

In the past I pushed the CO2 up to 55 mg/l. I indeed never had 65 mg/l.

For now, I am planning to keepn this insane amount of CO2. let' see...

greets,

yme

 

[yme]

thanks Tom as well

greets,

yme

 

[Tom Barr]

We came to the 45ppm range as a a slow progressive dosing using the CO2 meter to get the desired plant growth/health in that large tank.

Beyond that for the discus, they started turning darker and showed some signs of stress. They are more sensitive and easy to tell than most any other fish IME with respect to CO2.

I would assume the pH or/and the CO2 meter be used more as relative measure, and then slowly and progressively step wise, I would add a bit more, say 2-4ppm for 1-2 week's at a time, and see the response of the fish and plants.

This is what I do for each and every aquarium, my own included.
The critical issue is doing it slowly and watching the plants.

Plants can take 2-3 weeks to respond. I've had BBA continue for 3-6 weeks after setting the CO2 in a good range.

There is a delay.

If you go too far, too fast with the CO2, you stress the fish.
I'd prefer never to have that occur, algae is easy for me to get rid of.
So I start low and work up slowly and step wise.

This means less fish stress.
Plants/algae are expendable really.

Fish are not.

So this method might prove much better at targeting the eyeballing the correct CO2 for the plants. I have found some correlation with the CO2 meter, much less with the pH/Kh chart personally, so I'd say it is a better method and more consistent.

Accurate?
Cannot really say with a reference for comparison.
Same old problem for NO3 and PO4 test kits.

We are not going to get around easily.

I would also see about the tap water, maybe run it through Activated carbon, or use some of the AC in your aquarium for awhile and see, SeaChem purigen etc.

The rest seems like CO2.

Also, when you check to CO2, make sure to see what it does that first 1-4 hours when the lights come on.

Here's the graph of a typical day for the the bememoth aquarium:

The points are 15 min data points.
The more sqaure/rectangle the slopes up and down are, the better, the less steep they are, the worst the CO2 system is.

A steep slope up and steep slope back down means the system is very responsive. This is for a very large aquarium also, for smaller aquariums, the slope should be even steeper.

If the drop off is extremely steep, then it means the aquarium can degas the CO2 rapidly also, and likely means there is a high O2 present.



Regards,
Tom Barr

 

[yme]

I always wondered about this chart.
For my tank, it takes about one hour to get the desired amount of CO2. But the slope after CO2 shut down after the lights are off, is really different. Allthough I don't have a monitor to see what happens during the night, I have measured the CO2 level in the morning. I don't remember the numbers exactly, but it was around 25 mg/l. Too little surface movement? I recently added an airstone to add a little bit of surface movement. don't know whether this makes a difference. If my CO2 level in the morning is still too high, how important is this observation? Your post kind of implies it is quite important. Anyway: it should be easy to change the setup.

greets,

yme

 

[Tom Barr]

This tank has a massive wet/dry filter, surface skimmers, air injection on a timer.
The CO2 is about 2-5ppm at night.

Note, the CO2 meter is very dependent on WHERE the probe is placed in the aquarium.

That part is somewhat relative and arbitrary for the aquarist, it's a big old ugly looking probe. Not something you want out in the middle of the tank etc.



Regards,
Tom Barr

 

[Tom Barr]

I always wondered about this chart.
For my tank, it takes about one hour to get the desired amount of CO2. But the slope after CO2 shut down after the lights are off, is really different. Allthough I don't have a monitor to see what happens during the night, I have measured the CO2 level in the morning. I don't remember the numbers exactly, but it was around 25 mg/l. Too little surface movement? I recently added an airstone to add a little bit of surface movement. don't know whether this makes a difference. If my CO2 level in the morning is still too high, how important is this observation? Your post kind of implies it is quite important. Anyway: it should be easy to change the setup.

greets,

yme

Well perhaps the meter is reading it relative, maybe you have a mere 37-25ppm = 12ppm of CO2.

I sort of doubt it, but you can check that too.

Regards,
Tom Barr

 

[Jeffrey Funk]

Have you looked at the Hach CO2 standards? Just browse their products by analyte and they sell two different NIST CO2 standards, 10000 ppm ampules & 100 ppm solutions (not sure what the packaging is for this). Perhaps this is what you're looking for.

 

[yme]

After a bit of airation, the level falls back to 1 ppm....

I never heard of the Hach stuff. I need to read about it

I think it is also wise to update my thread as well.

greets,

yme

 

[Tom Barr]

Well, seems about right then.

The issue of CO2 off gassing once you use the references.

Regards,
Tom Barr

 

[Biollante]

Hach, Purveyor of Quality Test Stuff

Hi All,

Hach, purveyor of high quality test equipment. https://www.hach.com/

I use the 100 ml solution https://www.hach.com/hc/search.prod...kLabel=Carbon+Dioxide+Standards+as+CO2+100+mg along with some ‘ultra pure distilled’ water.

I have another system and had folks with a system designed for the beverage industry which they claim some ridiculous degree of accuracy do some comparisons.

All seem to agree pretty close, in fact my old Hach Carbon Dioxide Test Kit, Model CA-23, Drop Count Titration, Hach - Carbon Dioxide Test Kit, Model CA-23, Drop Count Titration even came, well, in the nieghborhood.

While these systems may not be up to lab standards, I regard them as reasonably accurate for most of our purposes.

Having said that I have some folks who say, for a price, will provide traceable standards for CO2 solution whatever concentrations we wish.

For what it is worth, I doubt your C-deficiency is CO2 related, but I am generally wrong about these things.

Biollante

 

[Tom Barr]

As soon as you pop any CO2 reference standard in gas or a liquid, it rapidly off gases and escapes to the air.

Unless you have a sealed method to use it and test it with the CO2 probe, the reference standard rapidly becomes a moving target, and.........the richer in CO2 concentration the standard, the faster the decline will be.
That's based on Fick's 1st law of diffusion.

Ambient is no problem, higher than that is going to be an issue.

I can make no O2 or CO2 references, ambient etc, but richer ones are tough without some sort of sealed chamber.

If you could evacuate the chamber with the reference, while having the CO2 probe there already to go sealed in the chamber section etc, then you could do it. Not many hobbyists would do that or find it anywhere near practical I would think.

Regards,
Tom Barr

 

[Biollante]

Khp

Hi,

The Hach reference solution is not CO2 but Potassium Acid Phthalate, KHP that acts as CO2 for purposes of the calibration.

Jeffrey Funk: Sorry I missed the question, the bottle is an HDPE, designed to pour the aliquot without introducing contaminates.

Biollante

 

[Florin Ilia]

This thread is three years old, has there been some progress in CO2 measurement? Is there a "modern" way to measure it precisely?

 

[Tom Barr]

Meter is good if you use references to verify the ppm.
Degassing and an IR also work well, but few hobbyists will use this ever.

I think just using the plants and eyes, providing a high level of O2, then very slow and progressively adjusting the CO2 up till there's good results is still among the best method. Problem is many hobbyists are too impatient, think their test kit/methods are the end all, for absolute unquestioned CO2 correctness.

This teaches what poor CO2 looks like as relative measure, not absolute concentration.
This relies on plants, growth, fish etc.........not some test methods directly.