# CO2 Drop Checker Solution



## Kimm8 (25 Feb 2020)

Dear UKAPS community,

I followed a DIY 4 dKH recipe here.
Unfortunately it ended up being 5 dKH according to my API test. Maths is not my strong suit, how may I adjust to make it 4 dKH? I opted for 1.2g baking soda and currently have 450mL of 50 dKH (after taking 50mL to make 5 dKH).

Edit: I also tested it using an Aquasonic carbonate hardness test kit, which turned yellow with 4 drops, indicating 40ppm according to the instructions.

Help much appreciated,
Thank you.


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## zozo (25 Feb 2020)

I wouldn't worry to much about the 1dKH difference in the drop checker.

See this graph, it reflects the colour-change related to CO² contents and the DC solution dKH value.





At the top row is the DC solution dKh value, the LHS is the colour the DC reflects at X CO² contents. In our case we like it to be 30ppm?
Make a cross-reference between 4dKH and 5dKH in the drop checker. And you won't notice a lot of difference in green. 

I do not know about your eye quality, but mine do not see the difference. If i had to read the DC only.



In both cases, if the drop checker is green you are in the correct range. 

https://www.ukaps.org/forum/threads/drop-checker-color-relation-to-kh-question.42795/


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## GHNelson (25 Feb 2020)

Try the below method from another UKaps thread.
This recipe has been given by Clive (ceg4840). So I am sure that the recipe works. 
Just mix 3 G of backing soda with 500 ml of distilled water. 
Then you just take 5 ml of this mixture you just made and mix with 245 ml of new distilled water. And that's it mate. 
There only 2 steps and it's only in the first step that you're adding baking soda.
hoggie


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## dw1305 (25 Feb 2020)

Hi all,





hogan53 said:


> Just mix 3 G of backing soda with 500 ml of distilled water. Then you just take 5 ml of this mixture you just made and mix with 245 ml of new distilled water. And that's it mate. There only 2 steps and it's only in the first step that you're adding baking soda.


I'd probably start again as well. Sodium bicarbonate is <"nice and cheap">, and you really don't want any <"errors with CO2 levels">. 





Kimm8 said:


> Maths is not my strong suit, how may I adjust to make it 4 dKH? I opted for 1.2g baking soda


I usually <"use a spreadsheet"> for all of these little calculations. The derivation of dKH is actually a <"bit strange">, but the 1.2 g in 1000 mL is correct: 





> the RAM of sodium (Na) = 23, the <"RMM"> HCO3 = 61 and the RMM of NaHCO3 = (23 + 61) = 84, 1dKH= 21.8 ppm HCO3 and 21.8 *(84/61) =30 mg/L of NaHCO3 = 1 dKH and 120 mg/L = 4dKH





Kimm8 said:


> Unfortunately it ended up being 5 dKH according to my API test.....I also tested it using an Aquasonic carbonate hardness test kit, which turned yellow with 4 drops, indicating 40ppm according to the instructions


Those people who know me will tell you that I have just taken <"a *very deep breath* and counted to 10">.

I'm not being funny, but you've just made up your solution with "Baking Soda" (which should be 100% NaHCO3) and RO water. Why on earth would the test kit give <"you a more accurate result">? 

You've actually just calibrated the tests kit with a "standard", a known concentration of (bi)carbonate ions, *any difference is inaccuracy in the test kits*.

cheers Darrel


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## Kimm8 (25 Feb 2020)

Thanks for the replies guys, I appreciate it. 



zozo said:


> I wouldn't worry to much about the 1dKH difference in the drop checker.
> In both cases, if the drop checker is green you are in the correct range.



You're right, it is difficult to distinguish between them 



hogan53 said:


> Try the below method from another UKaps thread.
> This recipe has been given by Clive (ceg4840). So I am sure that the recipe works.
> Just mix 3 G of backing soda with 500 ml of distilled water.
> Then you just take 5 ml of this mixture you just made and mix with 245 ml of new distilled water. And that's it mate.
> ...



Cheers mate, will give it a go.



dw1305 said:


> I'm not being funny, but you've just made up your solution with "Baking Soda" (which should be 100% NaHCO3) and RO water. Why on earth would the test kit give <"you a more accurate result">?


No worries, I had it laying around so thought I'd give it a go since it's never been used, no harm done right. 
In fact, I actually attempted it again afterwards and used your recipe here Darrel, but ended up getting 5 dKH again. 
Perhaps I should just wait until I have access to graduated cylinders and read meniscus or just purchase the solution.


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## dw1305 (25 Feb 2020)

Hi all, 





Kimm8 said:


> Perhaps I should just wait until I have access to graduated cylinders and read meniscus or just purchase the solution.


You can do it all by weight. Because these are fairly dilute solutions you can assume one mL of solution weighs one gram. 





Kimm8 said:


> In fact, I actually attempted it again afterwards and used your recipe here Darrel, but ended up getting 5 dKH again.


I know a lot of web sites and advice on the internet pushes water testing, but this is totally the wrong way around, you have a *known value*, but you are doubting your experimental method because the *method of estimating that value* gives you a different reading.

You will have to bear with me, but here is the same scenario in a different context:

I *owe you $50*, but when I come to pay up *I only give you $40*.

You say "*where is the other $10?*" and I take the forty dollars back, put them on a weighing scale and *they weigh 10g*, then I look up a book of figures and say "_*no that is definitely $50, I've looked at the book and the book says that 10g = 50 dollars*_".

Initially you aren't convinced, so I weigh the money again, same result and according to the book our debt is cancelled and you walk away happy that you've got your money back. I hope that makes sense.

cheers Darrel


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## Wookii (26 Feb 2020)

dw1305 said:


> Hi all, You can do it all by weight. Because these are fairly dilute solutions you can assume one mL of solution weighs one gram. I know a lot of web sites and advice on the internet pushes water testing, but this is totally the wrong way around, you have a *known value*, but you are doubting your experimental method because the *method of estimating that value* gives you a different reading.
> 
> You will have to bear with me, but here is the same scenario in a different context:
> 
> ...



Damn those new plastic notes!


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