Aquariums for discus should be kept within a temperature range of 26-31 C ( 82-86 F); a temperature of 29 C (84 F) is thought ideal for adults. Babies and young fish should be maintained at 31 C (86 F) degrees. The water should be very soft and slightly acidic; a pH of 5.5 - 6.5 is considered good for wild caught discus.
Captive bred fish adapt very well to harder water and to pH up to 7.2, except when attempting to breed, in which case soft and acidic is best, although it is preferred by the fish anyway. VERY clean water with frequent large volume water changes is necessary for the health of these fish. Never use pure R.O. water or distilled water as some "salts" are necessary.(ie;calcium,magnesium, etc) 100 ppm GH is average. New fish should be quarantined for a minimum of 4-6 weeks in a separate room, separate tank, and separate water changing equipment to eliminate the possibility of bringing in an infection to established fish.It is generally accepted that new fish should be added after "lights out" or during normal feeding.
Water quality must be very high, as discus do not tolerate pollution of any sort very well. A good tank will be equipped with a high capacity biological filter and be fully cycled (which usually takes a month or more.) Ammonia and Nitrites should be kept at 0 ppm. Nitrates should also be kept as low as possible. Weekly water changes are important, except in the case of a very heavily planted tank with high nitrogen compound grounding capacity and a very small biological load.