# Does anyone use the JBL Direct CO2 test kit?



## jaypeecee (16 Dec 2018)

Hi Folks,

Does anyone use (or tried) the _JBL Direct CO2_ test kit? I am referring to the following:

https://www.jbl.de/en/products/detail/6449

I decided to try this kit as it gives an instant (well, 5 minutes) measurement of dissolved CO2. I thought it was worth a try as I get frustrated waiting for my DC to change to lime green. The test kit is of the colorimetric type - in other words, colour matching with a control tank water sample. But, like all such tests, it's open to interpretation. Consequently, I'm never sure if I underestimate or overestimate the correct reading.

Has anyone else tried this kit?

JPC


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## oscarlloydjohn (16 Dec 2018)

Yeah, I used it once and it's been sat in my cabinet ever since. It is very difficult to read, and I find measuring pH drop manually gives much more accurate results. I don't think that it takes into account other acidifying compounds such as tannins so it gives an inaccurate reading.


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## jaypeecee (17 Dec 2018)

oscarlloydjohn said:


> Yeah, I used it once and it's been sat in my cabinet ever since. It is very difficult to read, and I find measuring pH drop manually gives much more accurate results. I don't think that it takes into account other acidifying compounds such as tannins so it gives an inaccurate reading.



Thanks for the reply.

When you say "I find measuring pH drop manually gives much more accurate results", does this mean that you measure the pH of the test sample after each drop of Reagent 2? And, if so, what pH are you aiming for? Do you happen to know what the reagents are? When measuring CO2, I'm only familiar with bromothymol blue but this kit doesn't appear to be using this reagent.

If this test kit fails to respond to other acidifiers, then that's a concern.

JPC


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## Andrew Butler (17 Dec 2018)

jaypeecee said:


> it gives an instant (well, 5 minutes) measurement of dissolved CO2. I thought it was worth a try as I get frustrated waiting for my DC to change to lime green.


Look into a PH meter; either spend out on a Hanna one for more accurate results or as many do a cheap one from Amazon or Ebay.
A Hanna one is about the best you can get and will give you accurate results but will set you back around £50.
Other people buy a cheaper one for less than £15 and just use it as a guide, I know @Zeus. has or had one of the cheaper ones so he might give you some input here.
With either of the above the results really are pretty instant, I'd never saying waiting 5 minutes for a test result is instant.
The drop checkers are more of a guide you can just glance at and most people on here would suggest doing a PH profile.


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## jaypeecee (17 Dec 2018)

Andrew Butler said:


> Look into a PH meter; either spend out on a Hanna one for more accurate results or as many do a cheap one from Amazon or Ebay.
> A Hanna one is about the best you can get and will give you accurate results but will set you back around £50.
> Other people buy a cheaper one for less than £15 and just use it as a guide, I know @Zeus. has or had one of the cheaper ones so he might give you some input here.
> With either of the above the results really are pretty instant, I'd never saying waiting 5 minutes for a test result is instant.
> The drop checkers are more of a guide you can just glance at and most people on here would suggest doing a PH profile.



Hi Andrew,

I already have an Extech pH100, which is a very good pH meter. I am fully aware that, in combination with the water KH, an estimate of CO2 concentration can be obtained. But the pH meter cannot distinguish between carbonic acid (from the dissolved CO2) and the other acids (e.g. humic/tannins) present in the water. So, the pH reading alone is not going to tell me the CO2 concentration, which is what I am trying to establish.

JPC


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## ian_m (17 Dec 2018)

jaypeecee said:


> So, the pH reading alone is not going to tell me the CO2 concentration, which is what I am trying to establish.


You can't determine the CO2 concentration from pH value alone, as you point out, the pH meter won't distinguish between pH due to CO2 or pH due to other acids/alkalis.

What you can do though is measure the pH difference before and after CO2 injection. Adding 30ppm CO2 to carbonate buffered water will drop the pH by 1 unit, regardless of the initial pH value. This is why many people talk about 1 unit pH drop by lights on being the value to aim for. Note the requirement for the water to be slightly hard (buffered), so a dKH of 4-8 is required for this to be optimal. Also the pH drop of 1 unit generally can tend to under read the CO2 level ie 1 unit pH is not 30ppm due to presence of other salts/acids/alkalis, but is a good start.

A drop checker is the way to go, as it is isolated from the tank water and will accurately indicate the tank water CO2 levels albeit with (sometimes) significant time delay. Part of the "art" & "science" of CO2 injection is getting a green/yellow drop checker at lights on. It takes a while, but in my opinion is the best and most reliable way of indicating CO2 levels without messing around with numbers and water samples.

Easy...too much CO2...whoops, well fish not bothered. Job done.


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## dw1305 (17 Dec 2018)

Hi all,





ian_m said:


> A drop checker is the way to go, as it is isolated from the tank water and will accurately indicate the tank water CO2 levels albeit with (sometimes) significant time delay.


I'm not a CO2 user, but that would be the relevant point for me.

Everything else is a movable feast, but with a drop checker you have <"empirically derived CO2 values"> for each level of carbonate hardness, only CO2 entering the drop checker, and that pH change indicated by the colour change of a narrow range pH indicator ("bromothymol blue"). 

It is a <"KISS solution">, the only issue is the time lag.

cheers Darrel


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## oscarlloydjohn (17 Dec 2018)

jaypeecee said:


> Thanks for the reply.
> 
> When you say "I find measuring pH drop manually gives much more accurate results", does this mean that you measure the pH of the test sample after each drop of Reagent 2? And, if so, what pH are you aiming for? Do you happen to know what the reagents are? When measuring CO2, I'm only familiar with bromothymol blue but this kit doesn't appear to be using this reagent.
> 
> ...



Measuring pH drop is basically the pH change between degassed and fully saturated. (nothing to do with the JBL test kit) 

This way, we don't have to estimate using KH values, which gives inaccurate results because of other acids. Instead, we just measure the tank's pH before the CO2 turns on (degassed) and then measure it at regular intervals throughout the day. You then find the difference between degassed and maximum gassed value and this is your pH drop.

A 1.0 pH drop is equal to 30ppm CO2. 

And yes, I don't think the JBL kit takes into account other acidifying factors. I remember reading in the instructions that you have to measure a degassed sample and then subtract that from the measurement with CO2. 

Oscar


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## jaypeecee (17 Dec 2018)

ian_m, Darrel & Oscar,

I am very grateful for your replies. They are all helpful. I have been grappling with this issue of measuring CO2 for some time. I don't like the hit-and-miss palaver associated with drop checkers but I do use one nevertheless.

Oscar, just a couple of points of clarification - when you refer to 'fully saturated', at what CO2 concentration does this occur? Is it safe for the fish? Also, is it possible to ensure that the tank water is fully degassed after lights out as the plants will be adding CO2 to the water overnight? Or does this not matter? I will check the JBL instructions when you say 'I remember reading in the instructions that you have to measure a degassed sample and then subtract that from the measurement with CO2'.

JPC


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## oscarlloydjohn (17 Dec 2018)

jaypeecee said:


> ian_m, Darrel & Oscar,
> 
> I am very grateful for your replies. They are all helpful. I have been grappling with this issue of measuring CO2 for some time. I don't like the hit-and-miss palaver associated with drop checkers but I do use one nevertheless.
> 
> ...



I should have been clearer. When I say "fully saturated", I mean the peak saturation of CO2 you get from your diffusion setup (varies from tank to tank), NOT the maximum amount of CO2 your water can hold. Depending on CO2 timers ect, some will reach this at the start of the photoperiod, others nearer the middle. My "full saturation" is 30ppm, others will have it slightly higher or lower. 30ppm is generally considered the safe level though.

It is not necessary to ensure that the water is fully degassed after lights out, it will gradually decrease through aeration as your solenoid would have shut off the gas supply. Most of us have the timer turn off the CO2 an hour before lights off to prevent wastage.


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## jaypeecee (17 Dec 2018)

jaypeecee said:


> I will check the JBL instructions when you say 'I remember reading in the instructions that you have to measure a degassed sample and then subtract that from the measurement with CO2'.



Oscar...you're absolutely correct. I hadn't spotted that. Thanks for bringing it to my attention. 

JPC


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## jaypeecee (17 Dec 2018)

oscarlloydjohn said:


> I should have been clearer. When I say "fully saturated", I mean the peak saturation of CO2 you get from your diffusion setup (varies from tank to tank), NOT the maximum amount of CO2 your water can hold. Depending on CO2 timers ect, some will reach this at the start of the photoperiod, others nearer the middle. My "full saturation" is 30ppm, others will have it slightly higher or lower. 30ppm is generally considered the safe level though.
> 
> It is not necessary to ensure that the water is fully degassed after lights out, it will gradually decrease through aeration as your solenoid would have shut off the gas supply. Most of us have the timer turn off the CO2 an hour before lights off to prevent wastage.



Thanks again, Oscar.


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## dw1305 (17 Dec 2018)

Hi all, 





jaypeecee said:


> I have been grappling with this issue of measuring CO2 for some time.


If you don't mind spending ~£100 for the meter, plus the running costs for buffers, 4 molar KCl storage solution, new electrodes (eventually) and you can follow the scientific protocol, then <"a pH meter is the way to go">. 

The problem is that they aren't "plug and play". 

cheers Darrel


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## jaypeecee (17 Dec 2018)

dw1305 said:


> Hi all, If you don't mind spending ~£100 for the meter, plus the running costs for buffers, 4 molar KCl storage solution, new electrodes (eventually) and you can follow the scientific protocol, then <"a pH meter is the way to go">.
> 
> The problem is that they aren't "plug and play".
> 
> cheers Darrel


I have an Extech PH100 meter, pH4 and pH7 buffers already. And you're right - they aren't plug 'n' play. The meter lets me know when a new electrode is required. Although chemistry is not my forte, I am a physicist. So I enjoy the science behind this fascinating hobby.


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## dw1305 (17 Dec 2018)

Hi all,





jaypeecee said:


> I have an Extech PH100 meter, pH4 and pH7 buffers already. And you're right - they aren't plug 'n' play. The meter lets me know when a new electrode is required. Although chemistry is not my forte, I am a physicist. So I enjoy the science behind this fascinating hobby.


Perfect.

cheers Darrel


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## Andrew Butler (19 Dec 2018)

jaypeecee said:


> Hi Andrew,
> 
> I already have an Extech pH100, which is a very good pH meter. I am fully aware that, in combination with the water KH, an estimate of CO2 concentration can be obtained. But the pH meter cannot distinguish between carbonic acid (from the dissolved CO2) and the other acids (e.g. humic/tannins) present in the water. So, the pH reading alone is not going to tell me the CO2 concentration, which is what I am trying to establish.
> 
> JPC



Hi Jay
I've learnt one thing in this hobby after trying to overcomplicate things to just stick with the masses and the simple rules they preach which you will read about time and time again.
I know it's not what you want to hear but it might be good advice.
Andrew


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## jaypeecee (24 Dec 2018)

oscarlloydjohn said:


> A 1.0 pH drop is equal to 30ppm CO2.



Hi Oscar...I'm not questioning your statement above. But I would like to understand why this statement holds true irrespective of KH. I'm obviously overlooking something.

JPC


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