Yes, use fractional pedaling. What you need to do is develop coordination and sensitivity between your ear and your foot. Practice with single notes first, across the entire range of the piano and be very observant of changes in sound relative to your foot movements. In fractional pedaling you only need very small movements to make large differences in sound, and it all hovers around that sweet spot in the pedal half-way between fully damped and fully undamped.
Watch the dampers as you pedal to see what they do. If you play a vertical remove the front panel. Watch, listen, observe. Try to get a sense of the mechanics of the dampers and what they are doing to modify sound.
It may also help your understanding by using your hand to damp the sound. What happens when you apply light pressure vs heavy pressure? What happens when you use one finger to damp a string versus the larger area of the palm of your hand?
As for the Nocturne, the main idea of the octave section is not the octaves themselves, rather it is the chorale tune. It is the chorale melody that is the most prominent layer within the octave section.