I know there was another recent thread on this, but mine appears to be different. I did the FC overnight test two nights in a row and got the same result. In the evening after the pumps shut down, I get a FC level of 8.5. The following morning, before the pumps kick on, or sunlight hits the pool, my FC jumps up to 10. I have no other sources of chlorine other than the SWG. I am wondering if it might have something to do with water temp. By the way, the reason I am testing is b/c my water is a touch cloudy. Can't really tell too much during the day, but when I kick on the lights at night time is when I can see it. It's not bad, and my wife says I'm crazy, but trust me it's there. All my numbers are good with the exception of needing to bump up the CH a touch. That number is currently at 200, which oddly enough has been dropping for a few months.