Keep your discus in acidic water. They are acidic water fish. Discus are very prone to bacterial infections. The lower your pH, the less chance of getting a bad bacterial infection. Keeping discus in alkaline water is probably the biggest mistake that hobbyists make. That's probably why they have such a bad reputation for being a difficult fish to keep alive. That's also why most discus wind up dying in pet shops. Pet shops usually have them in pH over 7.0. Just read the disease section of most discus message boards. The people with all the terrible bacterial problems are the hobbyists with their discus in water with a high pH. You wouldn't keep an African cichlid in low pH, don't keep a discus in high pH. Lower your pH(6.0 - 6.5) and see how much happier and healthier your discus will be.