Please help me save my Peace Lily. I'm more of a black thumb than green, but I love this plant. Purchased a couple of months ago from a supermarket in a biopot that didn't have holes. Within days the few flowers started to brown. I cut them as per instructions I found online. Green leaves continued to brown/yellow. I repotted in a ceramic pot with hole using Miracle Gro Moisture Control. The roots were plentiful and white, but root bound. There was no dirt outside of the roots.

Things have gone downhill from there. There was a time it looked great, but then the leaves started to turn brown and yellow. I was watering once a week, but the Moisture control, seems to make the dirt drier so I don't know how often to water anymore. And now there are powdery white spots on the leaves. But not spider-web like ones, I've seen described elsewhere. Are these from bugs? Is it okay to put the plant back into the holeless bio pot?

Thanks for help.