What kind of error are we looking at with DIY dkh test solutions? I've got a gallon of distilled water on hand, a pH test kit, KH test kit, digital scale to the 0.1 g. I'd rather not make 5L of 40dkh solution and then dilute.
If I was to make 500mL of 4dkh solution based on adding a small amount of baking soda, test KH, test pH, add more as needed.... By doing it this way I could estimate a 4 dkh solution pretty easily. I mean, effectively, the drop checker goes blue, green, dark green, yellow - it doesn't seem exactly precise, more of a range of CO2 concentration - Low, Good, High.
So again, I ask, how precise do you have to be to make the 4 dkh solution?
btw, I intend on making a drop checker from a vinyl hose & nailpolish jar, seems pretty simple.