To successfully keep Discus I believe you must first quarantine them for two to four weeks. When I kept Discus, I always quarantined with the lights off and if the fish showed any signs of distress from parasites I treated with a product called Hexamit from Aquarium pharmaceuticals. Keep the temp between 82 and 86 degrees. At temps above 84 degrees its difficult for parasites to live. I've always had success feeding freeze dried blood worms and mini cichlid pellets that sink. Also, you shouldn't keep any fish with your Discus that prowl at night, such as catfish or loaches. Keep something with them that would be found in they're natural habitat such as medium sized non-aggressive tatras. I've had luck with lemon tetras, black neon tetras, and harlequin rasboras. As far as water parameters go, a ph between 6.8 and 7.2 is ideal, but many Discus are raised and sold in higher or lower ph. Unless you want to keep wild Discus you don't have to be too concerned about ph as long as you avoid large fluctuations. Higher ph water has more buffering capacity then lower ph water does because of the salts, just avoid going to high. The more stable the environment, the better for the Discus. So, keep up with 25% water changes per week and enjoy your Discus.