When I first started with Discus I used Peat Moss in the tank and it did a great job of lowering the ph and reducing the hardness. As I learned more I realized my Pidgon Bloods and Marlboro's were so far removed from wild fish it was totaly un-needed as my tap water is 7 out of the tap and right in the middle as far as hardness....so didn't need it.
Wild cought fish are a different story and will IMO benifit from replacating the Blackwater they came from if trying to get them to breed. If you use an R/O system and then age the water using Peat Moss you can come very close to duplicating the natural waters of these fish. Then have an ample supply available for water changes.