Could it be PH?
I know most fish adapt to PH between 6-8, mostly 7 in aquariums. My BF (not Bow Front, even if descrption fits...
) and I had tried angels/neons 2-3 times before we got our last few. Those first 2-3 times, all the angels and neons died on us shortly ...
After further researching and talking to various fish keepers and fish store staff, they all recommended low PH (5.8 - 6.5).
My BF, Gary, (and no, he doesn't meow, he barks!
: ) has been keeping his PH at 6.5; I keep mine between 6.8-7 because of other fish in the tank. Our angels and his neons in the same tank w/ his angels have been looking very healthy and happy for the last few months.
Just our experience with angels and enons. Others may have been keeping their angels and neons at 7 or 7+ PH and have no problems with them. Who knows.... Hopefully, you could find out what was wrong.