Permanent Co2 Test....

[plantbrain]

You folks should not be using the KH test kits to make the Reference solution!!!

If you make a reference solution, you need to add a certain weight of chemical to a known volume of DI water(or pure solution etc).

So say adding 4.9923 grams of baking soda (heat to about 300F for 1 hour to drive off water and CO2 that accumulates in salts) to 5 liters will yield a reference solution of 40KH.

Take 10 mls of this, add 90 mls of DI water= 4 KH.
Note, you can make any number of KH references from this concentrated stock solution.
If you add a small amount of baking soda to a small volume, then the error goes way up unless you have very accurate scales and volume measurement pipettes!!!

So if you use more volume and more concentration, the errors go way down.
Then you need not be so accurate and anal.
50 liters is a bit impractical, 5 liters is not bad.

Many can get a 0.01 accuracy scale (fairly cheap), I have a 0.001 at home and 0.00001 at work.
Then you can send off a 100mls etc in a small bottle to friends etc so they can make their own.
Graduated cylinders are fairly accurate, pipettes are more so.

For each 10X magnitude dilution you increase the accuracy by 10X essentially.
There are practical considerations etc, but it's a better way to do it.

http/www.cnykoi.com/calculators/calckh.asp

Play around with this.
Try different volumes and different KH's and see how accurate the baking soda weight needs to be to achieve good accuracy.

Do not use a KH test kit which is not calibrated to make a solution.
You compare the reference solution to the KH test kit, not the other way around!!!!!

Here's more on dilutions so you can make whatever KH reference solution once you make the stock solution:

For diutions:

http/www.wellesley.edu/Biology/Concepts/...metovolume.html

This should get more of you off the duff and try this method out and see it's not hard and it's a lot more accurate. Many look and see, but need it laid out to actually try it.

So both methods avoid chemical stuff that scares you most, and all you do is add baking soda. DI water and make a drop checker of wrap the pH probe etc in a DO membrane and KH ref solution.

From here you have a very accurate method to measure CO2.

Regards,
Tom Barr

 

[MoreCoffee]

Cheers Tom,

I've been following VaughnH's method of mixing a solution, but any way to improve the accuracy of the solution is worth using. I assume the 4.9923 is the dried weight after baking it to remove moisture and Co2.

I think I'll probably end up mixing another solution using your method, But I do have one question.....

I'm not sure how most people would use this, but I want a visual refernce to show I'm in the 30ppm ballpark (+/- about 5ppm). I'll be monitoring the tank (fish/shrimp ect) for signs of stress due to overdosing.

The drop checker colour change will be useful to show any fluctuations (yellow / blue) in Co2 levels.
I dont think I'm looking for 'exactly 30ppm' ...... I doubt I'd get that level of accuracy without using your PH probe method. But this still relies on the inaccuracies in visually judging a colour chart ......

So the question is ......... Whilst using the drop checker method, does using 4.9923g (as opposed to 4.9g or even 5g) and the baking in the oven etc make a big difference to this method when it comes to taking the Co2 reading by judging a colour change ?

( Obviously with your PH probe/membrane/reference solution method the PH reading is far, far more accurate, so it makes perfect sense to get equally accurate KH levels )

Thanks again..

Al

 

[plantbrain]

It depends on how accurate you want to be.
The more significant figures, the more accurate your measurements are.

If 5ppm either side is fine, 4.99 ought to do it.
You do not need to be accurate to 1 mg in most cases and the cost for aq scale that will measure to 0.01gram is relatively cheap and ought to be a good standard for us.

So 5 liters+4.99 grams baked for 1 hour is not a bad method.
5 liters needs measured well also, but a volumetric flask or cylinder etc ought to do well.

For taking a sub sample of the stock solution, make sure to make 10-100mls of it, so you are afforded the same accuracy improvement rather than 1 ml unless you have a very accurate pippette etc.

Regards,
Tom Barr

 

[George Farmer]

Makes perfect sense now. The KH kit was bugging me re. accuracy. Thanks Tom.

 

[MoreCoffee]

It depends on how accurate you want to be.
The more significant figures, the more accurate your measurements are.

If 5ppm either side is fine, 4.99 ought to do it.
You do not need to be accurate to 1 mg in most cases and the cost for aq scale that will measure to 0.01gram is relatively cheap and ought to be a good standard for us.

So 5 liters+4.99 grams baked for 1 hour is not a bad method.
5 liters needs measured well also, but a volumetric flask or cylinder etc ought to do well.

For taking a sub sample of the stock solution, make sure to make 10-100mls of it, so you are afforded the same accuracy improvement rather than 1 ml unless you have a very accurate pippette etc.

Regards,
Tom Barr

Thanks again Tom

For me at least, having an easy, permanent visual reference that the tank is around 30ppm (+/- approx 5ppm) is ideal. As long as I can be fairly confident that I have a good Co2 level, that the level of Co2 is stable, the livestock are not in any trouble and the tank remains free of algae, I'm happy. (easy to please huh !)

Part of the reasons EI is so appealing is that it negates the need to test and measure things to a fine level of detail. So where possible I'd like to avoid having to measure bicarb out to 4 decimal places, especially if still relying on a colour chart.

....... I suppose it comes down to the difference between reliable monitoring OR accurate measuring of Co2 levels !

In my case, if the drop checker can monitor a constant level of Co2 (28ppm or 32ppm ... I'm not too worried) and alert me to any fluctuations then it's doing it's job as far as I need it to do.
Even if it takes 2 - 3 hours to react to variations, thats certainly quick enough to avoid algae issues due to falling Co2 levels and probably quick enough to avoid overdosing problems.


George,

.............
This is my only query. Unless the Nutrafin KH kits have changed then 1 drop reagent = 10ppm KH. This is obviously more accurate than 1 drop per dKH as there's 17.9ppm per degree. A minor niggle but for those with Nutrafin kits that may have lost/not read their instructions.........

I've checked the Nutrafin KH kit instructions and you are right (as usual )
1 drop = 10ppm. You add 1 drop at a time until you get the yellow/lime colour you multiply the total number of drops by 10 to give you the KH value in ppm.

I have no idea why I posted 1 drop = 1dKH ...... especially as I used this KH conversion calculator to verify my 4dKH when making the solution
http/www.hagen.com/uk/aquatic/ghkhconvcalaction.cfm

Apologies if that caused any confusion ...

Al

 

[George Farmer]

George,

.............
This is my only query. Unless the Nutrafin KH kits have changed then 1 drop reagent = 10ppm KH. This is obviously more accurate than 1 drop per dKH as there's 17.9ppm per degree. A minor niggle but for those with Nutrafin kits that may have lost/not read their instructions.........

I've checked the Nutrafin KH kit instructions and you are right (as usual )
1 drop = 10ppm. You add 1 drop at a time until you get the yellow/lime colour you multiply the total number of drops by 10 to give you the KH value in ppm.

I have no idea why I posted 1 drop = 1dKH ...... especially as I used this KH conversion calculator to verify my 4dKH when making the solution
http/www.hagen.com/uk/aquatic/ghkhconvcalaction.cfm

Apologies if that caused any confusion ...

Al

No worries mate. As Tom suggests, no need for the kit anyway.

 

[plantbrain]

I do think the drop checker is great for most folks, some want more and the pH probe method is suitable.
Scales can be bought on ebay for about 10-20$ not sure about the UK, but if you are resourceful, someone around has a scale and can borrow it from them.
0.01 accuracy for a gram is all you need.
A decent voumetric flask would be nice for the dilutions etc as well.

That's about all you need for making all sorts of reference solutions, not just KH.
So you can really test really well then and really focus in on things if you want to.
Otherwise the KH drop checker is a simple device.

Some are fine with using the KH test kit to make the solution reference.
It's about an error of 20% per unit of KH, less if you use a Lamotte test kit(about 5-10% then).
The weigh method is perhaps within 1%.

For good general horticulture, you likely only need 20% of the KH degree.
Which is about 5-7 ppm either side of the measure.

Regards,
Tom Barr

 

[RadaR]

Corr, what a read this is. Brain hurts but Im sure ill grasp it.

So is this best way to test CO2 then at the moment? Is the pH drop of 1 method far off from this methods accuracy.

 

[MoreCoffee]

Thanks Tom,

I have to say that if I had a PH probe, I'd be trying the probe/KH solution method a try, but maybe I'll keep that for later
As it is I'm going to get another 5ltrs of distilled water and mix up a more accurate batch of solution
using your method.

Thanks for all the info .....

 

[MoreCoffee]

Ok, Here's a quick update having tried Tom Barr's method for mixing up a solution.

I used some digital scales to measure out 4.99g of bicarbonate of soda (baked) and measured out 5ltrs of Di water. If you buy a 5ltr container from the garage, dont 'assume' that it contains exactly 5ltrs ..... mine certainly didnt !

I took the measured 5ltrs of DI water and mixed in 4.99g of Bicarbonate of Soda to make a 40dKH stock solution. I then diluted this down to make a 4dKH reference solution and added a few drops of PH liquid reagent. This went into the drop checker and then into the tank ......
Within 2 - 3 hours I was pleased to see a nice bright green (30ppm) CO2 indication.

(Another drop of PH reagent has since been added to give a clearer green indication)

I think Tom's method for making the reference solution will be much more accurate.
Measuring larger quantities of water & bicarb leaves much less room for error.
Having tried both methods, I certainly found it far easier to mix 5ltrs of water and 4.99g of bicarb than trying to adjust the KH of 100ml of water !!

A few notes/observations:

Tom's suggestion of baking the powder to remove water & Co2 obviously works. Initially I baked 7g of bicarb, but afterwards I was left with less than 4.5g, so I had to bake off more bicarb. I'd suggest anybody trying this should bake off about twice as much as you think you'll need .... bicarb isn't expensive and it saves another 3 hours of baking

As soon as I added the PH reagent there was a distinct difference.
My initial ref solution went blue with a PH approx 7.5, but with Tom's method it turned purple for PH of 10.

Putting these measurements through Chucks calc showed the following

Initial ref solution 4dKH & PH 7.5 = Co2 4ppm
Tom's ref solution 4dKH & PH 10 = CO2 0ppm

I left some of the new 4dKH ref solution in a jug overnight and checked it in the morning and the PH had dropped to about 8, I presume this was because CO2 from the air had diffused into the solution
Obviously the baking removes a good deal of CO2 from the solution.

So this morning I decided to check the PH of my old solution and the new solution.
Spot the difference !!!!

The one of the left is my original solution, on the right is Tom's method.
I can assure you Tom's is far more purple than it looks in the pic, either way the difference is clear!

This is certainly the method I'll be using from now on ..... good job, I've got a sealed container with almost 5Ltrs of 40dKH solution to get through

One last point ... I used a Nutrafin KH test kit as a double check on the solution and it showed 4dKH, however I have less faith in test kits than I used to have !

Thanks to Tom for posting this method

Al

 

[George Farmer]

Top stuff mate. You are a credit to this forum and to the hobby.

How long does the solution last in the dropper?

 

[MoreCoffee]

Top stuff mate. You are a credit to this forum and to the hobby.

How long does the solution last in the dropper?

Thanks George
........ Really the real credit goes to those that came up with and improved on this method, my limited brain power only allows me to imitate not innovate !

As for how long the reference solution lasts .... Well I can't actually answer that just yet.
Since first wanting to try this method I've mixed up 3 different batches of reference solution, increasing in accuracy each time. The first was just a quick test to see if I understood what it was all about, ending up with Tom's method ( tho one I'll be using from now on)

However from reading comments on other forums, I believe the solution in the drop checker will last for a few weeks (I'm guessing 3 - 4), but the stored 40dKH solution should keep for a considerable time as long as it stays sealed.

Al

 

[Themuleous]

Nice work Al if its really as easy as you make it sound I think I should get off my lazy ass and try it. BTW what did you use to weigh the bicarb? Guessing of everything this measurement needs to be the most accurate, and is the 4.99g after you've baked it for 3hrs?

Sam

 

[MoreCoffee]

Nice work Al if its really as easy as you make it sound I think I should get off my lazy ass and try it. BTW what did you use to weigh the bicarb? Guessing of everything this measurement needs to be the most accurate, and is the 4.99g after you've baked it for 3hrs?

Sam

Sam,

It is quite easy as long as you've got the scales. I'ts well worth a go !

I measured out both the water and bicarb, I used some digital scales, accurate down to 0.01g to weigh the bicarb. The 4.99g was the weight after baking. We also have a quite accurate 500ml flask, so I used that to measure the DI water.

Once I had the 5ltrs of 40dKH, I measured out 90ml of DI water and 10ml of 40dKH to make the final 4dKH reference solution.

Al

 

[Themuleous]

Right oh, might give it a try! Will be needing a drop checker now too! How much were those ADA ones again....

Sam