Which temperature for Discus?
Is it by all means necessary to keep Discus fish at 28 °C water temperature?
Do they become ill or do they feel unwell at 27 °C?
it is actually possible to keep discus at temperatures from approximately 25 °C upwards, it is only important that you do not lower the temperature too quickly.
The plants actually grow better at 27 °C, don't they?
It does not make too much difference for most common aquarium plants as long as temperatures do not rise to/above 30 °C.
It is nevertheless advisable to keep the water temperature at the lower end of the recommended range: Every additional degree requires higher heater performance and accordingly causes higher electricity costs! The temperatures must of course never be lower than tolerated by the fish, so please do not overdo energy saving!
Dr. Bodo Schnell