m0useanswered grow question a year ago They definitely look like a mite, but they don't look like the typical spider mite. also the typical mites that infest cannabis are on the underside of the leaves not in the soil. They also are a bit bigger and have spots on them, coined two dot spider mite.
They are most likely some kind of soil mite eating and praying on other organisms within the soil itself. If you have not noticed any issues with the plants I would ingore them. You can wash the medium with some pesticides or better yet miticides/acaricides.