I have a ficus macrocarpa that is cycling leaves. It grows new leaves, and drops the larger older leaves. The cycle lasts about a week or so. The base of the tree is always covered with fallen leaves. I don't think that I am under watering. It could be light, but I'm not sure how many lumens ficus needs. It receives 14 hours per day of artificial light. The light is adjusted toward the UV / Blue end of the visual spectrum. Red light light is slightly attenuated. The Ficus is in a greenhouse. Temperature is very steady at ~75 degrees, humidity is about 45 percent. The ficus is potted in a standard bonsai mix that is fairly pores. The plant is watered when it appears to be slightly dry. The mix of leaves is about 60% old leaves, 40% new tiny leaves. growth seems strong. Fertilizer is Bio-Gold, changed every month. I water with water that has been adjusted and filtered. Chloring/Chloramines are filtered, and pH is adjusted to 5.5-6.5. I also have two Chinese elms that were very strong, but are slowly dropping leaves. No disease is evident on plants and only a few flys on tack boards. All maples seem to be stable and healthy. Any ideas why leaves are dropping?