@Frederick: yes, I would feed, as Bernd says, living black mosquito larvaes, not frozen.
@Bernd: oh I hope so to see your breeding plant ( Zuchtanlage) in September! My tanks look more like Fredericks, and I have no idea how to do else ….
Phoenicurus still show no breeding now, only the one time at the beginning … and that’s often so, when you get new fish …