If you use a drop checker with a reference solution of KH then there is absolutely no reason to raise the KH of your tank just to make it easier to read your CO2 levels. You can buy some of the pretty (and expensive) ADA ones, the ADA knock offs (a bit less expensive), or even the plastic ones by Red Sea (least expensive). All work well, but some look a little nicer than others. You can even DIY one if you're handy and want to spend even less money.
You place the reference solution in the drop checker which is higher than your tank water but won't mix because of the design. The CO2 will then diffuse into the reference solution and level out at the same levels as your tank. It interacts with the pH solution turning it a shade of yellow, green, or blue which indicates whether you have too little, not enough, or too much CO2. The exact levels are determined by your KH reference solution which can be adjusted depending on what your target CO2 level is.
