Discus are slower picky eaters when you first get them. Having to compete against faster fish like danios, angelfish, and rainbows, makes it harder to get them to eat. Some plecos have been known to chase discus and try to "clean" off their slime coat. If you are looking at smalller discus, they also should not eat a lot at one time, so you have to feed them more often.
They like to school and should be kept in groups of 4-5 minimum. I keep my tank at 84-85F. Higher temperature water has less O2 so aeration and flow is important but discus also require areas of calmer water within that tank.
If you really want to keep discus, I would double check your water parameters and consider getting rid of some of those faster fish. Keep a mostly "amazon" tank with just the tetras, rasboras, rams, SAE, and cories.