Any lower than 82-84, they are more easily susceptible to developing parasitic diseases. If the Discus seem stressed in any way, or if you suspect disease, the first step is to slowly raise the temperature to 88 to 90 degrees, before administering any medications. For more details on disease diagnosis and treatment see the Disease section on the main menu. Chlorinated tap water will kill the established bacteria in filter sponges and cartridge frames. If you have any disease, it may be transferrred to the other tank.
Some pet stores use the same water circulated between all their tanks.
This means any disease is transferred to all the tanks. You will know your Discus are healthy and happy if they come to the front of tank when you come into the room or, at least near the tank. Don't keep a Discus tank in a hallway, a child's room or any other area with frequent heavy traffic. They are very sensitive to vibration and will jump and be stressed at any hard noises transferred to the tank. Discus also like, according to the experts, a tank that is not too low to the floor.