The white film is most likely powdery mildew. You can prevent it with sprays of a labeled product such as neem oil, potassium bicarbonate or bayleton.
Hibiscus needs lots of sun, consistent moisture, and moderate nutrition to bloom well. If you haven't fertilized this season try applying a quarter cup of lawn fertilizer sprinkled around each plant and then watered in well.
Thanks for the question. Please stop in again soon!
Q&A Library Searching Tips