trust me... as long as you are diligent in keeping your water clean and are willing to spend the extra time to do that you are more than half way there...
About doing water changes from the tap- supposedly in most areas this is fine and even beneficial. The chlorine increases the conductivity of the water.... Some Altum Angelfish keepers are starting to do this to ward off parasites and disease.
i think discus that have been removed like 20 generations from the wild should be used to our waters to be honest, especially those bred in asia. i cannot imagine that asian breeders will be using anything other than tap water. no offense to them (me being one of them ) but R/O probably is not used extensively in the discus farms in asia...
so mine is straight from the tap. i do daily water changes of around 20-25%. the fish have been doing fine for the last couple of weeks as well.