Mauldydaft, Can you take a little better photo of the spotting under the leaves? It's no quite clear enough to tell exactly but it appears to be scales developing. They often start under those little soft shells. Try cleaning the leaves of all the white stuff by soaking a cloth or paper towel with rubbing alcohol & get all those things off the leaves. That's a start. As to too wet or not moist enough --- I'm not good with inside plants so I'm not the best to tell you. Hopefully me posting on here will bring this to the attention of someone who can help you more.
