Your ideal readings for chlorine are determined by your CYA level...see the link in my sig for the "best guess chlorine chart" for more information there. With a CYA around 30 or so ppm, a FC of 12.5 is a little high, but you can swim in it--I just wouldn't wear a brand new bathing suit. And, in a day or so, that level will have dropped down closer to the "recommended ranges" for chlorine for that CYA. But I certainly wouldn't panic over it......