Why does my Hibiscus Have Brown and Yellow Tips?

Hi Judy, I inherited this hibiscus this winter. Previously it had been fertilized periodically with Miracle Grow. When I got it, it had this leaf problem, which I thought might be fertilizerPlants need fertilizer only when they are actively growing. Slow growing plants in low light require very little plant food. Too much fertilizer is worse than not enough. Most plants prefer a water soluble plant food at 1/2 the recommended strength. Plants that are in bloom or dormant should not be fertilized. Houseplant food contains nitrogen (N), phosphorus (P), and potassium (K). A fertilizer containing these elements in equal proportion is considered a balanced plant food. Nitrogen helps in photosynthesis and encourages the growth of leaves and stems. Potassium and phosphorus also help in photosynthesis and aid in root and flower development. Most fertilizers have trace elements of other minerals that are lacking in the soil but are necessary for good plant growth. Fertilizers have a high salt content. If a plant is not producing new leaves and doesn’t absorb the fertilizer, salts build up in the soil. These salts can burn the roots, discolor the leaves, and cause new growth to be small. burn. So I have been primarily watering with filtered water (our water has a lot of chlorine). It was looking better, particularly after I trimmed it back, but the leaves are still browning. It is an old hibiscus, 5 to 9 years old I guess.
Can you tell me what is causing this problem? There is a good bit of new growth as well.