| To my eye it looks like it could be mite damage of some kind. I have had good success against spider mites with Safer's Soap. But spider mites usually have webs too. If you haven't found any webs it may be a different type of mite. I dont' think washing with water is sufficient to remove them. Other members will be able to tell you how they have gotten rid of them. Until you treat the plant I would isolate it somehow, away from your other plants.
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