What could cause the sample to turn turbid or begin effervescing after the addition of the DPD reagent?
Turbid or Effervescing sample after adding DPD
Samples with high alkalinity might turn turbid or begin effervescing. Check the alkalinity of the sample. It is common for samples over a pH of 7.6 to have alkalinity of 250mg/L and above. When adding DPD, you should get a pH around 6.3. High amounts of bicarbonate can cause small bubbles in the sample, causing false high readings. If possible, pretreat water to a pH of 6-7 before testing.