I have a 50 g aquarium that has been established for many years. Over that time, I have had angelfish that have all grown to be large and beautiful. Before the virus set it, I bought a young angelfish to replace one of my older ones that have died. This one is staying small. Why? It seems to be an ordinary koi angel.
I have a feeling that your small Koi Angel is on the bottom of the dominance level among the large Angelfish. Are you distributing the food in several different areas of the aquarium so that the smaller Koi has a better chance of getting more of a beneficial share. Also I find that future growth of Angelfish is determined on how well they are fed as fry and the amount of growing room they have in their tank. I say this as I hatched some Koi fry just before I had to spend several weeks away from home. I usually started my fry on newly hatched baby brine shrimp. These fry had to be raised by a family member on strictly " First Bites ".
This packaged food did have acceptable results however my fry are much smaller then ones previously raised. Good luck with your newcomer .
Interesting. Yes, I spread the food around. The two seem to be buddies and hang around together a lot. The large one definitely doesn't bully the smaller one. Both seem healthy.