OK, I essentially got the answers I was looking for from a guy at our local mom and pop pool store. He told me a couple of things. 1. when you shock, initially the Cl goes up, but as it interacts with the water and the nasties within, it comes down to acceptable levels after a short period of time. The regular shock that you put in during the evening and run the filter overnight, the pool should be okay for swimming in the next day. The quick shock that you can swim in after 15 mins or so, it's just that. And for comparative measure, he told me that your typical large public pool, like a YMCA pool or hotel pool, has a much greater level of Cl to account for the large number of bathers. He told me it's typically around 7-10ppm, if not more. And we've had our kids in those pools often. So I think that I should be okay with sending the kids into the pool even when the Cl reading beyond 4.0 on the test kit, provided I follow the directions on the particular type of shock that I use. I'll still aim for the ideal reading between 1-3, but won't fret if the Cl registers 4.0 or above at 10am on a hot, sunny Saturday.