Ozpaph, I control regularly with a magnifying glass, in this case I could remove the oldest leaf and used a mikroscope. Therefor I'm sure it is the family Tenuipalpidae. It looks like Tenuipalpus or Brevipalpus but that is already guesswork.
I was not able to remove them mecanically without damaging the plant itself, so I used Acequinocyl. All individuals were dead but there are still eggs. In two/three days I'll spray with fenpyroximat to avoid resistances. The other plants on the same board are treated as well.
If you have any advice, I'm glad to hear about. I'm really terrified of spidermites.
Michael