You should not be losing any chlorine overnight. Pollen and debris falling into the pool can use a little chlorine, especially during the spring pollen season, but not normally very much even in the spring. Nothing else should be using any chlorine overnight.
When measuring the overnight loss, you need to keep testing error in mind. The FAS-DPD test is +- one drop. So, losing up to 1 ppm, when doing the test so it reads in steps of 0.5, could just be normal testing variation.