Your zamioculcas needs more light, not more fertiliser. You could also try repotting the plant.
This could indicate that you have regularly given your zamioculcas too
much water. Place your zamioculcas in a spot with more light to give the
soil a change to dry out.
It sounds like the ends of the stems have been burned by the sun. Move
your zamioculcas to a spot where it is not in direct sunlight.
If you have any additional questions, contact us at info@zamigo.eu