Repeat the overnight test again tonight. Wait until the sun is off the pool this evening. Test, add bleach, and then an hour or so later test again. Then, test again early tomorrow morning before the sun is strong on the pool. Compare that to the last reading from tonight. See how much you lose.

With a CYA of 50 and as hot and sunny as it has been lately, I think I'd add enough bleach in the evenings to get to around 7ppm. That should keep you from dipping below 3ppm by the next evening.