I'll almost guarantee you that if your feed your corals with a filter-feeding food they'll be much better in a month or two. You should feed them at least once a week. Dramatic temperature swings could also be your problem. Also check for any potential predators that only come out at night. You may have some sort of worm that's become huge in your system and it may be forced to start feeding on corals due to lack of other food. Still so many possibilities after water parameters but feeding your corals more often can only help. Good Luck!