Angel Fish Fry

[GuppyLover]

I have 2 Angel fish fry which I believe to be between 1 to 2 months old. One of them is growing like crazy while the other is still the same size as when I got her. She eats plenty and doesn't get picked on by the other fish and I have no idea what is causing her to not grow. When I picked them out I specifically picked the smallest one (Being the one who won't grow) but she hasn't grown since I bought her.
Thanks in advance

 

[WhiteDevil]

Ive had about 20% of my angel fry never grow past the 4-5 week mark, mine ate well to but did eventually perish.