Re: Healthy or unhealthy culture?
If I am seeing it correctly, that looks like feces peppering the inside of the cup. Mites tend to be on the move, in my experience but they are about the same size. They are opaque as opposed to mites being a little transparent, too.
When my cultures get that black mold in there that it looks like you have, they aren't usually producing at 100%. Not sure why that's in there, but for me, it was that I was adding yeast and vinegar to a commercial medium that already had the anti-fungal/mold under control without me meddling. When I stopped adding that stuff, I have had much better results and no more black mold. They sure smell better, too... Not sure it's the same stuff I had, but it's possible.