I use the TF-100 test kit. Whenever I am testing for chlorine, whether it's free or total, I have noticed that as it sits it reads a higher level. In other words, when I first drop the 5 drops of test in the tube it is pale yellow, within as little as 10-15 seconds it is brighter yellow (or, is already reading a whole point higher). Same with the pink of the free chlorine. I could add a few drops of the test and it turns clear and stays that way for many seconds after swirling, then I look back at it a minute or so later and it's bright pink.
So, my question is, when is the best time to record the correct reading for chlorine? The second I am done swirling the test tube, or 10 seconds later, 20...???
PS. I use a salt water system, but shock and increase with bleach.