Who Gives A Fish Forums

One more vote for Harlequins here. They're underrated. Super peaceful, easy to feed, and they don't hide like some Tetras do. Mine even swim up to greet me during water changes, which is kinda cute.

Cardinals are stunning but yeah, they need stable water. Your params sound good though. They'd do well with your Angelfish too, since they're from similar habitats. Just acclimate them slow, they're sensitive to quick changes.