I'll go bump it up a degree, but all my internet searching is saying 82 - 88 tops. Not doubting your experience, just not finding the sources.Discus do much better at temperatures 86 and above. Many discus aficionados keep theirs at 92-94 degrees. Below 86 and their metabolisms slow down and they are more susceptible to disease. I've kept mine at 92+ for years, but had too much trouble finding other appropriate tankmates at that temp. They are now currently at 86'.