My lemon tree is showing pale spots where she looks like the green part of the leaves are missing. The plant is about 2 years old and has been inside and in a south-facing window. Pot has drainage and I added citrus-specific fertilizer spikes a few months ago. She’s had fungus gnats before and responded well to treatment (hydrogen peroxide solution). But those didn’t do this kind of damage to the leaves. One branch seems to be more affected than the others. Please help!