Not hard at all. They can and will adjust and thrive in virtually any pH level. Water hardness doesnt matter either. The 3 key elements in keeping discus are warm water, good biological filtration, and frequent water changes. Discus prefer water temps in the mid 80's. The more biological filtration you have, the better. I always suggest good sized wet/dry filters on discus tanks as they provide the ideal biological filtration capacity needed. The water changes are among the most important. You can get by with 50% 1-2x a week fairly easily, just reduce stocking levels and feed clean foods. But if you really want to see the fish grow fast, daily water changes are recommended. Also, the source of your discus will determine if you succeed or fail. Discus from your LFS are generally in poor shape to begin with and arent worth the money for sickly and stunted fish. To do well, get discus from a local breeder, or buy from a mail order breeder/importer with a good reputation. This will make a world of a difference in your discus experience.
-Ryan