No pH of the tank should not matter. If the dKH fluid is in that bulb, CO2 will diffuse from the tank into the dKH fluid (which would be at it's own pH) and alter the pH, thus altering color. To make it there are a few sites online that show how to. I make my own using laboratory scales at my research lab haha
Basically you mix and dilute baking soda and distilled water a few times. The numbers escape me at the moment though.