You should read the background texts (left menue) more carefully or read our articles (e.g. in AMAZONAS or elsewhere or the book on Parosphromenus by Finke and Hallmann).
Everywhere it is clearly said that these fish occur in slowly flowing waters, not in still waters. But I have always said, in the book and in articles, that I never have used any filters and other water current producing equipments in my tanks. You can breed them very successfully pairwise in small tanks without any water current.
Nevertheless, I always recommend a small sponge filter for safety reasons.