Can you post a full tank photo? I'd like to see the sword plants in particular. They might just be emersed grown and losing their emersed leaves.
Still doesn't explain the wisteria turning black though. Can you tank another pic of that plant only? A photo that shows more of the plant. Ideally I'd like to see which leaves are turning black, the older or newer ones.
The grass like plant at the end doesn't look aquatic, do you remember what it was called when you got it? Grass type plants like that don't do well when trimmed half way down the leaf like that. They tend to die back from the cut end.