ficus problem is building up

Hi

I have read directions from this group about how to take care of ficus. I have them in a porch where they get all day indirect light, I water them only when the soil is dry and I don't move them around.

The problem is that from the last week their leaves are starting to have some spots. I also have the impression that very little flies fly around them frequently, which I haven't noticed before.

I have 2 pics of a leaf (underside and top side)

Could somebody give any directions? If more pics or other info is needed, let me know.

Thanks for all the info I have already found in here :-)