Hi poncirus,

here are some new pictures:

I would think fungus maybe? Tree looks wonderful :)

To be safe spray it with a fungicide for edible plants and you will do fine.

could be plant edema

John can you please explain? I have absolutely no clue

Google plant edema citrus; it happens when conditions are such that the roots absorb more water than the leaves can transpire. It is a condition that never occurs with in ground trees; so I don't have a lot of experience with it.... but it looks like what you have.

Oh god, hopefully is edema and not some fungus that could attack mu entire collection.

I already try to spray my tree with a fungicide called "safer defender". It's a fungicide with sulfer and I didn't see amy improvement. Do you think that I should tru a copper based fungicide just to safer? Thank you for your input!

No, dear... a fungicide is a fungicide; and in your case is probably overkill. I don't see any fungus indicators.

Oh thank you so much everyone. I will sleep much better this night knowing that my citrus doesn't any other treatment.