Kumquat leaves discolor

LazyMechanic starts with ...
Hi everyone, i am new to this forum and i have a kumquat, actually it belong to my auntie. The tree was around 4 years old and never has any fruit. I try to bring it back to life this year and i notice its leaves color doesnt look right to me, the leaves look like this for 6 months. I gave it some zinc and magnesium spray, nitrogen, also i mixed some trace elements with water last month, then epsom salt with water and pour around the drip line last week, but none of that help :) i hope someone here more experiences can tell me what wrong with the tree. Thanks

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