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dKh and Drop checker

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Genahanney

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7 Aug 2023
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Russia
Hello, the instructions for the ADA dropchecker say that it can be used in water with dKH 2.
1 question Why is this so? Farther. Other dropcheckers say that they show the correct value only for dKH 4. It turns out that you need to recalculate for other values? How to do it correctly? As a result, how to measure CO2 in an aquarium with dkH 3 using a dropchecker?
Thank you.
 
According to the ADA instructions, you need to use water from the aquarium for Dropchecker and it seems logical to me, because everyone in the aquarium has their own dKH. However, some people think that you need to use water with dKH 4 (prepare it specifically for the dropchecker), but what's the point? After all, Dropchecker reacts to carbon dioxide, which lowers the pH?
 
Hi all,
Genahanney said:
However, some people think that you need to use water with dKH 4 (prepare it specifically for the dropchecker), but what's the point?
Click to expand...
I'm not a CO2 user personally, but the reason for the solution of known dKH in the drop checker is because of the known relationship between CO2 content and pH change. <"CO2 Measurement Using A Drop Checker">
Genahanney said:
After all, Dropchecker reacts to carbon dioxide, which lowers the pH?
Click to expand...
It does, the <"protonation state"> of the narrow range pH indicator ("Bromothymol blue") indicates the pH and only gases (like CO2) can diffuse across the air gap in the drop checker.

cheers Darrel
 
What is the logic of using dKH 4 in a dropchecker if we need to see the pH change taking into account dKH in our aquarium?
 
Genahanney said:
What is the logic of using dKH 4 in a dropchecker if we need to see the pH change taking into account dKH in our aquarium?
Click to expand...
Can you post a copy of the instructions from ADA? You should never use aquarium water as the colour-change indicator in an drop checker - the checker always gets pure water with a well-defined KH, usually 4.0 for most applications. In principle you could use 2.0 KH drop checker solution if you wanted greater ability to discern aquarium CO2 in the 5-25ppm range but you would then lose the ability to discern levels between 30-50+ppm, and that's what people usually care about because that's the range in which problems with livestock can arise and you want to be able to tell when you have the CO2 gas turned up too high.
 
What is the point of using dKH 4 if, for example, 3 is in the aquarium and with this value dropchecker will lie, saying that co2 is not enough?
 
Genahanney said:
What is the point of using dKH 4 if, for example, 3 is in the aquarium and with this value dropchecker will lie, saying that co2 is not enough?
Click to expand...

4dKH is typically used in drop checker solution because the target green solution results when there is around 30ppm CO2 in the tank water column, which is the common target for most CO2 injected tanks.

The drop checker won't lie, the KH of your tank water is irrelevant, if you inject enough CO2 into the tank water to achieve 30ppm of dissolved CO2, that CO2 will diffuse into the airgap inside the drop checker, and turn the indicator solution the correct green colour. That will happen the same way if your tank water is 0dKH or 8dKH.

I've no idea why on earth those instructions suggest using tank water with the indicator solution, that would be the completely wrong way of doing it, and would not give consistent results between tanks. The KH of the indicator solution needs to be fixed and known, so it's colour change can be accurately linked to a known level of CO2.
 
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LOL this ADA product is ridiculous. This implies that you must have a 2dKH water in your tank for this DC to work as intended. Why didn't they just provide the proper solution with a fixed dKH with the vial they provide?? ADA always have to do things the other way...
What I would suggest is that you prepare your own 4dKH (or 2dKH if you prefer) reference solution and use that to add it to your DC. The content of that ADA vial is most probably pure Bromothymol blue.

4dKH Solution

Hello I have been read about solutions of 4dKH for the drop checker but they all are a little big in the amounts of water to use. I dont want to be left with 4 or 5 L of a 40dKH solution. So i scale it down to this: 500ml Distilled water + 0,6gr sodium bicarbonate = 500ml solution 40dKH...
www.ukaps.org www.ukaps.org
 
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Hi,

Genahanney said:
What is the primary source talking about the need for dKH 4 in dropchecker?
Click to expand...
There is no need for 4 dKH; it is just practical to monitor CO2 around 30 ppm in an aquarium with CO2 dosing, and that is what you get with 4 dKH. You can set it to 2 dKH, and you will monitor CO2 around 15 ppm. It is the dKH/CO2 ratio that matters, the ratio will determine the pH and therefore the color in the dropchecker.

Here is a reference for colors (pH --> color):
en.wikipedia.org

Bromothymol blue - Wikipedia

en.wikipedia.org en.wikipedia.org
 
Genahanney said:
And what if you don't pour water into the dropchecker at all, but pour only the reagent?
Click to expand...
The buffer with KH (actually bicarbonate) is required so that the pH would be dependent on the CO2 levels. The reagent itself probably does not contain any bicarbonate (or any buffer), so it will not provide any useful information.
 
Genahanney said:
And what if you don't pour water into the dropchecker at all, but pour only the reagent?
Click to expand...
I am a total noob who only installed my Fzone CO2 generator this morning, So, I could have this totally wrong, but I believe that the reagent supplied with many of the lower end drop-checkers is already pre-mixed with a 4dkh reference sample. The confusion this is causing me is how I came to find this thread.
 
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