The general rule is sub adults will get stunted if they do not have 0 ammonia 0 nitrite and very low nitrates(<20 is usually the bar I believe?).
The little guys are usually on a BIG feeding regiment, with messy foods so you have to change the water a lot.
When I had 50 cent size fish I changed 60% of the water daily when I could.
Others will chime in but I know some breeders will change water multiple times per day to get the fry started out right.
What are the actual size of your fish.