Why is there white stuff on my hibiscus plant and how can I get rid of it?

The white stuff on your hibiscus plant is likely powdery mildew, a fungal disease that can affect plants. To get rid of it, you can try spraying the plant with a mixture of water and baking soda, or using a fungicide specifically designed to treat powdery mildew. It's also important to improve air circulation around the plant and avoid overhead watering to prevent the spread of the disease.