The graph on the right is from the week of February 18, 2013. I wanted to show a "chemical event" to give people an idea of what these sensors can do. As you can see, my hot tub was is terrible shape, high pH of around 9, very low ORP, and I had turned the temperature down to 80, to save energy, because I was not using it. I then tried to shock it with chemicals and I turned the heat up. These graphs are on a one week time scale. I lowered the pH, and increased the ORP, but not to the desired level. I am afraid I have to drain the hot tub and start over with new water, or try some pH down and more oxidizer. Any suggestions?