What would cause a sample with Chlorine to start pink and then become clear?
DPD pink color turns clear
Too much chlorine can bleach the color from the DPD, causing the meter to read lower than expected or zero. Samples with high concentration of chlorine, over the concentration range, will have a visual pink color only briefly (flash) and then turn clear, resulting in a zero or under range measurement. If the smell of chlorine is present in your sample, this is probably what’s happening. Try a sample dilution using deionized water and repeat the test. Keep diluting the sample till the results are within the range of the kit or method. Multiply results by any dilution factor created.