According to the information ive read on so called Discus forums you can acclimate Discus to a goldfish bowl.
Being that I am a person that strives to do things to the best of my ability I keep my Discus in soft acidic water. This means around 3-5 GH 0-1KH and well anything under 7.0pH but over 5.5 or 6.6 depending who you talk to.
Having a Discus tank is OK with soft acidic tap water. Having a planted Discus tank IMO you need VERY soft water because of all the fertilizers. The fertilizers + moderatly hard tap water IMO is too hard for Discus. I start at 0ppm total disolved solids.
Exactly what is it you want to know?
RO is for (fresh & clean
) soft water. If you have soft tap water and your tank's hardness isnt skyhigh then why bother? I use a RO unit because it does everything for me.
I would tell you to get information from the breeder who supplies your fish. I would also tell you to find a breeder that keeps Discus in soft acidic water...
Yah BTW heres my Discus when I got em. According to some Discus forums out there...they wont grow out in a planted tank.
Here they are three months later...nice little comparison here...the smaller Discus were the same size. The larger Discus are 6 months old here. The smaller ones are three months old.
another three month shot of daddy. and my algae I had to battle. co2 fixed that.