I have a related question ... I just got my test kit from tfktestkits, and I notice that the color of the solution (spa water plus drops) changes over time. So, if I read the chlorine and pH right away I get one set of values, but if I put it down and come back a couple of minutes later the colors darken a bit and I get slightly higher readings for both. After that the colors stabilize and don't change at all. So which reading is the correct one - the one right after adding the drops, or the one I get a couple of minutes later?