Hello Stefanie,
I use the same method as you “the just do nothing-method” and it works. The populations are growing slow. I always had problems with feeding very young Paros. Many died after feeding Artemia salina or Turbatrix aceti as a result of an increase of bacteria (I think). Hiding in a dense layer of Salninia they prey on smaller food for the first week and this food seems to be better for their health and growth. After one they eat Artemia salina (feeding once per day).
Greetings
Patrick