Powdery substance, brown spots on Maxillaria

[Vrana]

So I'm finding my new found orchid hobby as frustrating as it is rewarding. Gah. Anyhow my latest issue is...

I recently noticed the Maxillaria Tenufolia I got a couple weeks ago is covered in a fine whitish powdery looking substance, which is concentrated toward the center of the leaves. It almost looks like dust, and when I wipe it off it turns a pale brownish-green color. Is it mold? A bug? What do I do about it? Unfortunately I didn't get a picture before cleaning it off (I wiped the whole plant down with q-tips soaked in a mix of water and hydrogen peroxide). My nearby plants don't seem to be affected, though I isolated it just to be safe.

I also noticed as I was checking on the roots that there's a p-bulb in the center, beneath the 'soil' line (for lack of a better term - it's planted in orchid bark mix with some sphagnum moss) below where the roots begin, that seems to be rotting. It's turning a brownish-black, as is the leaf coming out of it. There's also some dry brown spots on a couple of the p-bulbs on one side of the plant. These were there when I got it, but should I be worried? Does the plant look okay otherwise? I'm very much a novice here...

I've included some pictures. Thank you in advance.

[Bud]

you are right, its probably mold....peroxide will kill it....
your Maxillaria have nice plump bulbs and the roots are healthy....one mechanical issue on one bulb looks like a small animal took a bite....the Phal leaf was also eaten and chewed upon but the roots are healthy....all you need to do is continue with your care ....you have the right instincts about your plants....good luck