@Peter:
I don’t want to propagate normal / commercial aquaristics. Of course we should not forget the weekly water change. (And you’re right, a 640l tank does not invite to do that.)…
I just want to try to give my fish a place where they can live as healthy as possible, because a tank is never as good as the real intact habitat… even the water – if we have just osmosis water – ro – water, we are not as good prepared for our fish as someone who has really good clean rain water or spring water with a low Calcium ….
And I see, that Marcin thinks also about that, how he can optimise the situation for his Paros …
@Marcin:
That dark colouring I also once had – with Phoenicurus in a small 25l breeding tank with just a „rucksack-Filter“.
I posted fotos, but nobody could help me with an idea. I just got the confirmation, that it would not be odium…..
I guessed afterwards that perhaps I used too much of „Aquahum“ (even less as Pawel advises in his blackwater-recipe)….