Permanent Co2 Test....

[MoreCoffee]

I've recently seen an article on Tom Barr's site (and others) discussing a method of making an intank permanent CO2 test using a reference solution with a known KH (4dKH in this case) to give a visual indication of 30ppm CO2 ....... Well it looked good and it looked easy to setup, so I had to give it a go.

All the hardwork involved in this method has already been done by others (Tom Barr, VaughnH )
Hopefully they wont mind me posting it here to make others aware !

....... If it's good enough for Tom Barr, then it's certainly good enough for me ! B)

Using this method you get a clear visual indication of your CO2 level in the tank as follows:
Bulb colour green = 30ppm
Bulb colour blue = Co2 too low
Bulb colour yellow = Co2 too high

Here's how it looks .......

Basically you need a glass drop checker, some distilled water, a tiny amount of bicarb of soda and a PH test kit. The hardest part is getting the reference solution with an accurate KH of 4 ... it needs to be accurate !

I know most of these drop checkers already come with a solution, but most have no instructions and you dont actually know that 'green' = 30ppm CO2.

How I mixed up the solution:
I took 100ml of distilled water and checked the KH with a Nutrafin test kit .... 1 drop turned it yellow.
I needed to raise the KH to 4 by adding bicarbonate of soda - but only very small amounts !!

I used the tiny measuring spoon that came with a Tetra NO3 test kit and added one measure of bicarb.
I then tested the KH ..... it had risen to about 2, so I added one more measure of bicarb, another test showed it was around 4dKH.

To improve the accuracy of the reading I then used 2 x the water (10ml rather than 5ml), therfore each drop from the KH testkit indicated a level of .5 dKH rather than 1.

After a few adjustments with water/bicarb, I ended up with a solution with a reading of 4dKH.
The drop checker was filled 1/2 full with the solution and a few drops from a Tetra PH test kit were added, the solution turned a bright blue colour.

The drop checker was added to the tank, within a couple of hours the solution had turned green (as in the pic). The depth of blue/green colour can be adjusted to make it easier to read by adjusting the number of drops of PH reagent added to the bulb.

Cheers
Al

 

[voo]

Sounds like a good test to me. Not sure how it works though, how does it measure the CO2 in the water when it doesnt touch the water? Is it just measuring the CO2 that is escaping from the water?

Which pH solution did you use? The low pH or high pH ?

 

[MoreCoffee]

....Not sure how it works though

Well I had to read through it more than once before I understood it enough to give it a try.
I now think I get how it works ..... but perhaps Tom will pass by and correct anything I've got wrong !

As far as I understand it ... the CO2 escapes from the tank water and is absorbed by the solution in the bulb, the Co2 level in the tank water and the bulb will equalise over a period of a couple of hours.

The reason for using a solution made up to a specified KH, is that in the tank other factors can influence KH. This will lead to errors when comparing KH/PH on the various charts

The PH of the solution will change as the CO2 is absorbed. Most PH test kits show a green colour for a PH value of 6.6. Using the normal CO2 charts you can see that a KH or 4 and PH of 6.6 gives a Co2 reading of 30ppm.

The KH of the solution can be adjusted to cater for different Co2 levels. For example if I change the solution to a KH of 5, then when the solution goes green (PH6.6) the CO2 reading is 37.

There have been a few threads recently about measuring CO2
I'm going to check my CO2 tomorrow using 3 other different methods and then compare the values.

First method: I'll check the KH and PH of the tank water.
Second method: I'll check the PH of the tank and take a water sample and check the PH after it has stood for 24 hours.
Third method: I have an old 'Red Sea' CO2 test kit sitting around (bought before I found out they were pretty useless).

It'll be interesting to see exactly what the difference is between the readings !

 

[voo]

Thanks for that, I understand it a lot more now, especially where the KH of 4 came from

 

[RuslanJamil]

How long does the indicator last?

 

[MoreCoffee]

How long does the indicator last?

I'm not sure, but I've seen it mentioned that it should be OK for a period of a few weeks.
But remember, I mixed up 100ml of reference solution, the rest (minus what was used for testing/adjusting the KH) is now is a clean, sealed bottle. So I have a stored KH reference solution and to change the mix is very easy.

I addition to the other CO2 testing methods that I've mentioned earlier, I've also been given an old JBL permanent Co2/PH test kit and have set this up as per the instructions and put it in the tank next to the glass drop checker.

The only thing is that the colour reference chart is missing !
If anybody has one could they tell me what the colours represent, or if it's available online, maybe even a scan of the chart .

=====EDIT=========
Just after posting the friend who gave me the JBL kit has just found the colour ref chart, so I'm sorted.
=================

The instructions sat that "+!" means CO2 too high, "-!" means CO2 too low. What it doesnt mention is what level of CO2 they consider to be too high or too low. (30ppm ?)

The JBL kit says that the indicator should be changed at least every 14 days.

I think the main difference between these methods is that the JBL one uses 1ml of tank water and some reagent as the reference solution. The instructions say the JBL kit can be used as a CO2 indicator " If, besides Co2 there are no other substance in the water which lower PH (eg peat, PH-lowering agents, nitrates)" ...... Most of our tanks will have nitrates in there !

As I see it, the method from the Barr Report has a number of advantages ...
> A known KH of the reference solution, not affected by anything in the tank water (other than Co2).

>Indicating a known Co2 level (30ppm), not just JBL's suggestion of 'too high' or 'too low' with no reference to the actual number of parts per million. (The main advantage as far as I'm concerned)

> Making a different KH reference solution means the drop checker can be used to indicate different levels of CO2 (eg at a PH of 6.6 the green colour would indicate 22ppm using a KH of 3 or 37ppm with a KH of 5)

> The distilled water and bicarb will make LOTS of solution much cheaper than buying replacement reagent.

> The glass drop checker looks far better than the plastic JBL kit

Hopefully I'll get a chance to test the water later today and can post the Co2 readings for the 4 different methods.


Cheers
Al

 

[MoreCoffee]

........ A bit more info.....

Having looked at the JBL CO2 colour chart, I think the big difference is accuracy.

Taking the PH and KH range measurements from the colour chart and applying them to the CO2 chart in
Chucks calc gives the following CO2 ranges ........ pretty wide !

PH KH CO2ppm
6.4 +! Too Low
6.8 4-8 19 - 38ppm
7.0 8-12 24 - 36ppm
7.2 12-16 22 - 30ppm
7.6 -! Too High

Using that indicator you could assume you have 30ppm but actually have a CO2 level as low at 19ppm or as high as 38ppm. All those ranges are down as acceptable (indicated by the tick on the chart).

A link to the colour JBL colour chart can be found HERE !

With the method Tom Barr has been disucssing I have a known KH or 4 (accurate to +/- .5dKH), so the range for CO2 should be far closer to 30ppm.

Now I have a pretty high level of confidence that this method works, what I may do is make another batch of KH reference solution, this time I'll use 4x the water for the KH test (20ml) so that each drop of KH reagent indicates a step of .25 dKH. That'll make the CO2 accuracy even greater.

Apart from the increased accuracy from a known KH value, I think this method is better becuase it uses distilled water not tank water, the KH of the distilled water has been adjusted ONLY by the addition of bicarbonate of soda. My tank uses ADA Aquasoil, known to impact the PH and KH of the tank ... any impact on those values will affect the Co2 reading !

Al

 

[Themuleous]

Very community spirited for you Al, cheers. This method certainly seems the most accurate, would be keen to see how it compares to the other three methods. I like the 1 pH point method, as it removes the fact that things other than CO2 in the water can affect pH as you're testing tank water both times, the only difference between them is that one has had its CO2 removed. Guess the only down side is that you dont know the CO2 of the air its 'sitting' in so you could have anything from 0.3 to 3% CO2 (as I understand).

Anyway, rambling now! Let us know how the other three tests work out.

Sam

 

[MoreCoffee]

OK I've now measured my CO2 using 5 different methods.

1. A drop checker using a reference solution of 4dKH (VaughnH's method from the Barr Report website)
2. Red Sea CO2 test kit (tank water + liquid reagent)
3. PH/KH (tank water + reagents - Nutrafin test kits)
4. JBL permanent test set (tank water + reagent in plastic drop checker )
5. PH difference between water in tank and tank water that has stood for 24 hours to 'degas'

The results ......
1. Drop checker with KH4 solution/bright green colour = 30ppm
2. Red Sea Co2 kit (liquid reagent type) = 64ppm !!!
3. PH/KH PH=7.0 Kh=13 CO2=39ppm
4. JBL permanent test kit = Co2 between 24 - 36ppm
5. PH of tank 7.0 PH after stood for 24 hour 8.0. Drop on 1 degree PH
(PH7 KH13 = CO2 of 39ppm PH8.0 KH13 = CO2 of 3.9ppm)

A few notes:
The CO2 level fed into the tank has not been adjusted for sometime, all my fish & shrimp (amano, plus a single bumble bee shrimp) are doing fine, no signs of distress. Therefore I'm assuming the Co2 level is not too high ...

I'm sure there is at least some degree on inaccuracy with all these methods, however as the method suggested by VaughnH uses a pretty accurate reference solution of 4dKH and is the only one that does NOT rely on tank water, my feeling is that this one is perhaps the most reliable.

Anything that relies on tank water can be influenced by other factors. My tank has ADA AquaSoil and PowerSoil as a substrate. These are known to affect PH/KH etc.

The Red Sea kit seems to be WAY off the mark ! If the CO2 were at 64ppm, my fish be dead !

The JBL kit covers a range that is a bit too wide, but it would be OK for 30ppm +/- 5ppm, so not too bad at a PH of 7.0. Just a pity it comes with a crappy looking plastic drop checker. It would be of less use at other PH values as it could show a CO2 level as low as 19ppm as being good.

I have to say that I like the drop checker / reference solution. I have a feeling it's quite accurate and gives a clear visual indication of the level of CO2, without having to test the water all the time.
It is currently a bright/clear green colour. Any sign it's turning yellow/green shows the CO2 is rising, if it starts turning blue/green my CO2 is dropping.

..... any thoughts !

Al

 

[voo]

Interesting to see the differences between the methods of testing, good stuff Would there be any advantage to using RO water in your reference solution instead of distilled? Also, how do you know when the solution needs changing?

This method seems to rely on there being as much gas escaping as there is in the water. Is this really what happens?

EDIT: Water surface movement is said to help release the CO2 from the water. Therefore if the water movement below the drop checker is faster, surely there will be more CO2 being released into the drop checker, resulting in a false, higher reading? Similarly, if there's less water flow the CO2 released into the drop checker will be less?

 

[MoreCoffee]

Interesting to see the differences between the methods of testing, good stuff Would there be any advantage to using RO water in your reference solution instead of distilled? Also, how do you know when the solution needs changing?

This method seems to rely on there being as much gas escaping as there is in the water. Is this really what happens?

EDIT: Water surface movement is said to help release the CO2 from the water. Therefore if the water movement below the drop checker is faster, surely there will be more CO2 being released into the drop checker, resulting in a false, higher reading? Similarly, if there's less water flow the CO2 released into the drop checker will be less?

Voo,

I know where you're coming from, but I won't pretend that my chemistry is good enough to be able to answer your (perfectly valid) questions.

I read about the method and was interested enough to give it a try .... From the various posts I've seen there have been a number of people on a number of forums trying to prove/disprove this, all of them seem to agree it's a perfectly valid method, and all of them (VaughnH, Gomer and Tom Barr) have a better understanding of the chemistry behind it than I do ! There are a number of posts about the method on APC and the Barr Report.

I can however say that if you look at the pic of the drop checker, the water level is up inside the horn, so the area in contact with the air gap in the drop checker has no movement at all.

....... I in doubt ..... give it a try.

Al

 

[Themuleous]

Interesting Al, am surprised to see the Red Sea kit working so badly and that the 1 point pH method works well.

Will be using that in the future. I guess the inaccuracy in testing ability is what lets the pH/KH chart system down, if you could measure both accurately (+/-1%) it would work well.

One quick question, how 'clear' it the solution when its green, i.e. is it obvious that its green and not say green/yellow?

Sam

 

[voo]

Is this the test that i was reading about where they hook up a pH meter to the solution to test the CO2 level?

EDIT: Why can't they just make a CO2 meter

 

[Themuleous]

Why can't they just make a CO2 meter

Dont think there is much point, as all you need are very accurate pH and KH test kits, get those right and you can work out the CO2 of the water with ease.

Sam

 

[MoreCoffee]

One quick question, how 'clear' it the solution when its green, i.e. is it obvious that its green and not say green/yellow?

Sam, You can adjust the level of colour by adjusting the number of PH reagent drops you add to the KH reference solution in the drop checker. I used about 3 drops from a Tetra PH test kit and it is a definate Green now it's in the tank. When I first added the drops to the solution it was a clearly recognisable Blue. I've not seen the Yellow (and dont really want to as it means too much Co2) !

Is this the test that i was reading about where they hook up a pH meter to the solution to test the CO2 level?

Voo,
It's very similar. The method with the PH probe is one that I believe Tom Barr is looking at, it uses a similar KH reference solution, but does away with the air gap of the drop checker to give a quicker reaction time.