Check the underside as well to see if visible insects.. use a magnifying glass to help see if you have spidermites. If so, you can buy any product for insects to use or make a mix of isopropyl alcohol of 50-50 ( water to alcohol) to spray out of the sun to treat insects. I like to use Bayer insect spray. It's a three in one that kills mites, and fungus etc,

Hope this helps,

Laura