Under-watering, over-watering, and too much exposure to direct sun and chemicals or salts in tap water can all result in brown leaf tips. Monitor your watering schedule – as a rule, water the plants once every week in spring and summer, reducing this to once every ten days in winter. Keep the plants away from direct sun and water them with rainwater or distilled water. Over-feeding can also cause this problem. Review your care plan and modify it as necessary.