To support lilnaugrim, I have relatively hard water, and I keep ember tetras with no issues. The males seem to colour up better (which is a shame, as I have mostly females :P ) but they cope fine with my relatively hard water. I've found no behavioural/physiological signs of anything being amiss because they're not in softer water. That said, I sourced my locally, but I just wanted to chuck the thought out there ;)
I've also got endlers, but they're not the favourites in my tank...the cories are, so if I were in your boat I'd probably add more of them! :P And I can't recall if they've been mentioned, but rasboras are very visually pleasing to me as well, particularly the Hengeli's and Harlequins. :D Good luck!