TEMPERATURE:
28 degrees Celsius is best, higher water temperatures seem to have an adverse effect on some discus. I have no exact reason why, but discus become very flighty to the point they dash about wildly sometimes leading to death. Also fertility drops as you reach 30 degrees.
 

We have experimented extensively with temperature and found far fewer problems and a better electricity bill at 28 degrees, than at 32 degrees which is often recommended.