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Hans and Hilda spawining. Be patient. For some, it may take a few minutes. Depending on the speed of your connection.
For those who have never witness it, will find it quite intreguing. The chasing action is more of a contant nudging from behind by the male. It's not like a territorial, chasing away an intruder kind of a thing. It's hard to describe. You'll have to see it for yourselves. There is no agression. Although they may make quite a stir, splashing at the surface and all. That's why all sharp object and ornaments should be removed from the tank during this time.