Disappearing chlorine...

[chem geek]

Taylor recommends that you stand outside with your back to the sun so that you shade the tube in front of you looking down into the tube. If you have the sun shining directly on the tube, you'll get a reading that is too low. If you do the test with insufficient lighting, you'll get a reading that is too high. It's a finicky test, especially compared with the titration tests.

[CarlD]

But, even more importantly is to do the test the same way every time. This allows you to track changes and mark progress. You learn over time if you are over- or under-representing the results and compensate.