White crystals mean a salt build up in the soil caused by overwatering. The cure is to flush the soil with water so that you see excess water running from the drainage holes. Do this several times in a row. Then do not water your houseplants so much in the winter. They go dormant and don't drink much.  Watering with distilled water can also prevent this build up of salt in the soil. Feel the soil and water only when the top inch is dry. Do not fertilize unless the plant is actively growing and then feed most indoor houseplant just once a year in the spring or summer. Many plant foods leave salts behind. Spring is coming and I predict your hibiscus will be just fine - if you stop giving it too much to drink! Keep growing, Marianne Binetti