I've read the pool school stuff a few times and checked out the recommended levels page as well.
I just have a question on when its "safe" to use the pool. Most place (other than here) say not to use the pool if your FC level is above 4.0 ppm. According to the recommended levels and the CYA chart, the target FC level for most is above 4ppm.
When shocking the pool to levels of 10+, when are you actually "safe" to use the pool again after shocking. What level do you need to let the FC get back down to before swimming and why are the target FC levels all above 4ppm if other places say not to swim in anything above 4ppm?