I've read over this thread, and I'll try to be objective. The only way to have success when keeping discus is to set up a tank specifically designed to meet there needs. Some background, preferably good planted area to encourage them to move about with confidence at first, and clear swimming space towards the front to aid with viewing them. Twice a day is a minimum to feed these fish, and if they're under 2" four times a day, in small enough quantities for them to clear quickly as good water quality, even more so stability, is very important. They are tougher than many believe, but will only thrive with a high,quality, varied diet, and a good consistent water quality. I would say a minimum temperature of 82 degrees with very good filtration. Two 25% water changes per week are also need. The main stumbling,block is that if diet or water quality, tank set up or positioning are not to their liking, they become stressed and then become susceptible to a whole host of illnesses.
The fish you have in your tank simply aren't compatible with discus, you have to decide what you really want to keep. Any aquatic shop with basic knowledge would not advise that discus and your other fish will do well in the same tank if their needs are to be met. Please go one way or the other. Soft water, acid loving species, or hard water. You'll have a better experience and less problems along the way