I have a 10 year old Fukien Tea bought in superb condition. It gets plenty of sunlight in a south-easterly window at about 70 degrees. I water when the soil seems to be dry on top, about once to twice a week. I have been noticing some inner leaves turning brown and dropping. What should I do? (im trying to avoid over watering or under watering)I mist it and have it on a humidity tray. Ive read many books on the species but am still confused as to what is wrong?