# Making 4dKH reference solution for Co2 indicator



## Philosophos (May 7, 2009)

With a TDS conductivity meter you're going to have something like +/- 10% accuracy. You can do better with diluting and an accurate scale. +/- 10% alkalinity at this range is going to throw your drop checker off by +/- 2.5ppm CO2.

And yes, drop checkers work on pH. Bromothymol blue is a pH indicator between 6.0 and 7.6. As the pH drops from diffusion of the air/CO2, your drop checker changes color.

-Philosophos


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## Left C (Nov 15, 2003)

Here is one method for making the 4 dKH (30ppm CO2) solution. It is the method that I used. There is also a little easier method posted somewhere on this forum.


billionzz said:


> KH standards
> 
> Here is the information needed to make a KH standard. When I started using the drop checker method for measuring CO2 there was a lot of confusion as to the proper way to make a KH standard. After a lot of searching and asking questions I found the correct way to make a good KH standard.
> 
> ...


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