Discus aren't that hard to keep however you need to pay extra attention to their water conditions as juvenile discus require clean water in order to grow. This is why most of us keep them in barebottom tanks with a few hiding places to keep maintenance easier. Juveniles need plenty of foods in order to grow. In turn, this obviously contributes too much wastes that quickly deteriorates the water quality. This is the primary reason where you learn most breeders do even as much as 80% water changes twice a day to cope with the water quality. Failing that, stunting becomes evident with disproportionately large eyes in comparison to its body size.
Adults can cope better with lesser water changes but this depends on how your water parameters go as far as food amounts and waste amounts are concerned. If you want to start keeping discus, please be sure to choose your specimens with your local breeder, not the local fish stores. I'd suggest a 55g minimum and 4 discus as the minimum number. If you do not want the hassles, get 4-inch specimens or bigger. Never keep discus in less than four in number. There is a tendency one will harass the other resulting in poorly conditioned specimens as the bullied victims starve or pine away from feeding.