Hi I have this little bonsai which did not belong to me I had to take care of it since the owner moved away to other country so I'm not sure what is the name of it but guessing should be ficus microcarpa. I have it almost four years now and have change the pot twice during this four years. And all this year's it didn't grow bigger as a height only had some more leafs growing. I live in dubai where the weather is quite hot and humid but keep my plant indoor. I water when I think the soil is dry that will be every two days almost but sometime between watering I just mist the soil lightly and the leafs. It's by the window which can get indirect sun most of the day.

But my plant had this spot which are growing in numbers and spreading to new and old leafs all together. U can remove most of them with just simple rubbing or with finger nails but some are harder to remove. Can someone please help me with this?