I tried using 1 litre of de-ionised water, some Tesco Bicarbonate of soda and a API KH liquid test kit. Oh and I used some electronic kitchen scales accurate to 1 gram.
Water weights 1Kg per 1Litre so dead easy to calculate volume using weight.
I put a tiny amount of Bicarb into 100ml of the water and it went to 20dKH so I added double amount of water. Then I halved it and added double again to get 5dKH with 200ml then I added 40ml to dilute it by 1dKH.
Only took me a few minutes to get a 240ml of 4KH.
But I guess it's not going to be that accurate? But will it be accurate enough do you think for a drop checker?
I took a double sample size of water using my API KH test kit and used twice the amount of drops. I got 8 drops to make it turn yellow.