Yes, I believe that the main issue for Paros with this tank was simply the substrate (the pond soil used contained lime, which I did not realise at the time). A friend of mine has a similar tank with an acidic substrate and has successfully bred good numbers of Paros sp ‘Sentang’ and chocolate gouramis in it without any intervention –
So it is possible, although I agree with Peter that a more controlled approach is generally preferable and obviously the more demanding species would need more particular care.