 Brown leaf tips can be caused by under watering, so check the soil and if it feels dry, water! With tropical plants, it can also be because of lack of humidity. So put them on top of a humidity tray or close to a humidifier. It can also be the cause of too much fertilizer or tap water. Some plants are too sensitive for chemicals and tap water, so make sure to use filter, rainwater or put it aside in a bucket for 48 hours to get rid of most of the chemicals.