I don't think discus are terribly difficult to keep, but they definitely require a commitment of a lot more attention than your standard FW community tank. Adult fish are often fairly hardy, but nice adult fish are very expensive. Juvenile fish are much cheaper, but as molliwopp points out, feeding and water change schedule has an enormous impact on not only their growth rate, but also their adult size. This is why you hear about some discus keepers doing daily water changes of nearly 100% for their young discus. Young discus must be fed heavily, and to maintain perfect water quality for them requires large, frequent water changes. I know someone that breeds show quality discus locally, and he changes all the water on his juvenile tanks every day... plus he feeds 3 or 4 times a day, something like that. It depends on what your local tap water is like, but as molliwopp said, a lot of serious discus hobbyists use RO water.
