Spotting on shiranui mandarin tree

[Variegation Nation]

what is causing the spotting on the leaves of my mandarin tree?

[Millet]

Looks like damage from insects.

[Ahuacatl]

Looks like soot, did you burn anything recently near the plants?  There is a sooty mold fungus that grows on trees attacked by sap feeding insects such as scale, mealy bugs and aphids. 

[Variegation Nation]

I didn’t burn anything and the tree has been indoors for almost 6 weeks. The spots can’t be rubbed off. I have noticed some spider mites and fungus gnats but have treated the tree for both. Suspecting the spots are from spider mites. Planning on treating the leaves with a foliar copper fungicide.

[Ilya11]

You have to wait until a new growth flush.
Already damaged leaves  are not supposed to become normal.

[Ckitto]

I have many citrus trees and somehow Shiranui is the only tree that has this type of damage. I am trying to find the root cause as well.

[Variegation Nation]

My tree gets these spots on green leaves. It eventually gets worse, the leaves yellow and then fall off with the petioles attached. I did have spider mites but have addressed that issue. Overall, the tree is stressed and the lush green leaves have faded except for the bottom leaves.