Recently a day after I had changed water in my discus aquarium then 5 died. I have therefore 1 left. This time the cause was nitrite (NO2) poisoning but not so long time ago the same thing happened also after water change. Then the cause of death was most likely lack of oxygen. I am therefore started to suspect that there might be something wrong with the water here in Luxembourg. Discus are more sensitive than other fish and are therefore more likely to die if some chemicals in the water would stress them and make them more vulnerable. I have decided to not get any more discus and focus therefore on other types of fish, such as Malawi and dwarf cichlids.