A while back I had these little white bugs that appeared when I watered my orchids. (I repotted my orchids from moss to Schultz Orchid mix.) I was horrified. I checked everything I could and was told not to worry about it. Well, they killed one of my Phals.

!!! I tried to save it, to no avail. I noticed that my other two plants were contaminated as well. I went into a flushing frenzy with my plants and rinsed my medium in warm water. I haven't had a problem since.
My question is has anyone else seen these little bugs and what are they? I check all of my medium that I use now and I pretty much "sterilize" it now before I even use it.