500 - 600cm deep, 50 litres per adult discus if you can do it. They like a lot of water over their heads and swim in the middle water column. Discus can be aggressive and therefore a group of 6 or more is best, 4 an absolute minimum. Pristine tank conditions will keep them healthy and good quality feed. Bare bottom tanks are popular for keeping them although they look great in a planted tank. Regular water changes are essential 2-3 times, 30-50%a week and when really small total water changes each day are required. If you have never kept them before I would recommend getting discus of at least 7cm size.