The breeder I bought my first discus from swore that, from his communication with all discus breeders, discus is best kept in bare tank with sponge filter. To say thet discus can't go with plants or gravel is a preference by most breeders but not absolute. I have seen many planted discus tanks in public aquariums, including one 3,000 gallon wild discus, altum angel and tetra tank in the Barns and Noble Book Store adjacent to the Baltimore National Aquarium. The tank is filled with lush plants that fill this 16 feet long, 6 feet high tank all the way to the top.