One of my houseplants is covered in what look like white flecks. They don't move - even if disturbed. I'm not sure they're actually even creatures - can't see legs - but they keep multiplying and leaves with a lot turn yellow and die. They're all over the top surface of the leaves and are easy to wipe off but keep coming back. I thought scale but aren't they shiny? These things don't look shiny. Any help in getting rid of them completely?