The water quality or lack a food was not the issue because the other fry were three times her size when my hubby accidently killed them by overfeeding. I know the water parameters were good, I tested like I do with all my aquariums. They were in a 10 gallon with a filter rated 10x bigger waiting to go to the pond. I think the issue was genetics. She was an obvious cull, with a visible tail deformity, that I chose not to get rid of. Just like people, fish come in different sizes and have different handicaps.