Just an update to the species.
Martin H. wrote to me that it should be P. cf bintan.
I have 12 fishes now with around 4 or 5 males.
I will put 2 pairs into my 300l tank with Sp. vaillanti, betta coccina and boraras to observe their behavior in a bigger habitat with different zones.
If there is somebody interested in a pair in berlin, just write me.