Are you interested in blackwater aquaristics or not? If you are, general aquarium forums don’t help at all. They care about normal tap water aquaristics and fish that are mostly not endangered at all.
If you want seriously explore the maintenance of blackwater aquaria, you cannot learn much from those site. Read our fundamental informations to be found in the texts of the menue at the left side, not in this forum. Ans read the book “Prachtguramis” by Finke and Hallmann, and you will discover a world different to that. I did not write that book without a background of forty years of theory and practice.
Personally, I have no filter at all in my 35 small tanks of 12 liters each. But a small sponge filter driven by air is not wrong. But weekly water changing is advisable nevertheless. The water must be near to destilled, without any calcium, the pH should be held constant between 3.0 and 6.0, according to the species. All experts have no problems with this. The dogmas of the normal scene are copied from the normal aquarium literature and that is totally ignoring blackwater aquarium keeping. Many of their doctrines do not apply to this. As do many of the products of the hobby industry.
Forget it if you are seriously interested in Paros. Think about if you are. If you are indeed, try with relatively hardy species first that are not extremely endangered.