If you make your own 4 dKH water be sure you start with distilled water, not tap or tank water. You don't need it to be extremely accurate. If it is between 3.5 and 4.5 dKH that is accurate enough. Fill the drop checker bulb with that, then add 2-3 drops of pH test reagent to that. The pH test kit has to be the one where the color chart goes from about 6 pH at yellow to about 7.5 pH at blue. That means the solution is a bromothymol blue indicator solution. If you add to few drops you get such faint colors it is hard to judge the color. If you add too much, the solution is cloudy and is again hard to judge the color. The goal is to get a clear solution, with easy to see colors.