Again...all myth and old skool teachings. I use water straight from my tap. 7.4pH and a GH of about 4...but I know countless people who raise discus in a pH of 8.2 and a GH of like 12!! Like I have said before, the key to keeping discus are keeping the tank clean by way of water changes and maintaining the proper temperature. 84-86 degrees is where you want it. And water changes dont have to be that laborous...set the pH to around 6.5 and have a wet/dry filter on the tank and stock no more than 1 fish per 10 gallons and you can get by with a water changes twice a week of 30% or so. And discus do NOT require feeding of Beef Heart. I know a lot of people who feed them nothing more than prepared frozen food from their LFS. Bloodworms, Brine Shrimp, Mysis Shrimp, Krill. They will even eat flake foods and other dry foods like Colorbits. Discus are not that hard. Just follow the few basic rules and you'll do awesome with them. Discus are A LOT more rewarding that an angel would be...besides, where is the fun in keeping a common fish??
-Ryan