I got this orchid about 2-3 months ago as my first orchid, it's a mini phalaenopsis. It came from Walmart so I repotted it as soon as I could, cut off the rotten roots and potted it in a bigger pot that has drainage and airflow holes, with fir bark chunks and sphagnum moss.
I think I saw some black on the stem when I did this but I can't remember, and don't know what a healthy stem should look like so I assumed the coloration was normal. It was doing pretty good I think, it grew several new roots and the leaves have been firm and healthy looking.
A few days ago though I noticed some black spots on the lower roots I used to determine if it needed water so I pulled the medium back and noticed rotten roots and a ton of black. I pulled it out, washed and sterilized it with peroxide, trimmed the rotten roots again, and applied cinnamon to the worst of the black. I've since washed the cinnamon off, let it dry completely again, and repotted it, trying to keep the stem above the medium but theres not a lot of roots out the bottom so its not very stable and Im unsure of how good of a job I did.
I'm using MissOrchidGirl as my main source of info, but I have no experience so I don't know what the chances of this orchid pulling through are, or even if Im doing things correctly.