- Rinse the test tube with the sample leaving a few drops of the sample in the tube.
- Add and then crush, the DPD No 1 tablet in the few drops of the water sample until the tablet is thoroughly crushed.
- Add the 10ml test solution, mix and seal the tube with the cap.
- Select Photo 7 on Photometer.
- Take the Photometer reading in the usual manner – see Photometer instructions.
- The result represents the free chlorine residual in milligrams per litre (mg/l). Stop the test at this stage if only free chlorine determination is required.
- If it is desired to measure combined or total chlorine residual continue the test on the same test portion. Select the ‘Follow On’ from the screen options to continue the
- If shock treatment chemicals are present in the pool, add one DPD Oxystop tablet, crush and mix to dissolve. Stand for one minute before proceeding.
- Add one DPD No 3 tablet, crush and mix to dissolve.
- Stand for two minutes to allow full-colour development.
- Take photometer readings in the usual manner.
- The result represents the total chlorine residual as milligrams per litre(mg/l).
- The combined chlorine residual is obtained by subtracting the free chlorine from the residual result from the total chlorine residual result:- ie Combined Chlorine = Total Chlorine – Free Chlorine