I'm growing 3 plants and one of them just stopped growing as much as the other two despite me offering the exact same treatment(and has light green le

This could be many things, just the sort, Im not as big as my brother for instance... Im smarter though :P. Your soil looks kinda wet, now if you watered on day of photo thats fine. But if you didnt it could be they are a bit waterlogged... You soil looks a bit dense. If its not airy enough roots have a hard time forming. So better to underwater in the beginning and not water whole pot.