Thanks for your help!
Peter, I agree with your arguments. I suspected that uprising will be difficult in such an large tank. Thats the reason why I asked and not acted! So I will put my fry and perhaps one male in a 80cm aquarium. The young fishes are not many and they are little, so I must not react quick. But at the moment I have problems with my second Paro male (25 l aquarium). The alpha male was/is breeding permanently. He is smaller than the other, but a lot more agressive. Now the second male becomes agressive too and he wants to be the alpha male. The fishes had a lot of fights during the last week, and lost some scales. If the fights become harder, I will put one of the males in an 60cm aquarium togeher with Poecilocharax weitzmani, but only to safe his life and not for a long time. Because P. weitzmani occupies caves too and I dont want to mix different species with the same ecological niche in one aquarium.
But in general, I think its possible to create stable water parameters in large(r), planted tanks. But I have only experience with soft water in a middle size aquarium that contents 200 l with a group of D. maculatus (clear water cichlids). The pH is stable at 5 and conductivity 20-25uS. Water changes every week 50 l.
Thanks for your answers!
Greetings, Patrick