Keeping chlorine level between 3-6 at all times was suggested based on your CYA reading of 50ppm, which is a great reading. If your CYA was at some other level, the suggested chlorine level would be different. Can't remember if we linked this for you somewhere up in this thread or not, but here it is again if I did. Our "Best Guess Chlorine Chart" explains the connection between CYA and chlorine levels. http://pool9.net/cl-cya/. (By the way, this chart is also found in my and Ben's blue signature blocks.)