I'm currently doing an experiment in school where we are testing the effects of cyanuric acid on chlorine levels. My group was planning to test the amount of chlorine through the use of DPD and a spectrophotometer. We found out that potassium permanganate is useful when coming up with a standard line to which we can compare our experiment results to. However, we are not sure what to use as our "blank" and what to do to the difference concentrations of potassium permanganate. We plan to add DPD and a phosphate buffer to our experimental chlorine water so would we add these to the potassium permanganate? For the "blank" do we use distilled water + DPD + buffer?