I have an ACE system and had trouble with getting the chlorine to read anything between 0-.5ppm I eventually was able to get it to work by 1)making sure the water was balanced 2) making sure I had enough salt. I used the inidicator screen and got my level to be at least to the middle of the green on the scale per advice from my dealer. 3) Based on some other posts, I manually added a bunch of cholrine to kind of shock the tub to make sure everything was clean. 4) ran Ace at level 5 usage. Everything is working well now, water is crystal clear and i dropped the usage back down to a 3.