It could have been but it depends on how many snails you had (sorry can't remember) and if the tank was cycled and how often you clean it out
But they'll be okay separated. Baby Blue will be much happier when there are other girls that Blue can pick on instead of her so that's why she's swimming around right now since she's not threatened by Blue ^_^
Adding more silk/live plants and hides will really help keep stress levels down in the big tank as well
so that's something you can do as well.
As for medicating, just follow the directions when you get it and it should be fine. Of course if something doesn't make sense or you need help deciphering it, go right ahead and ask here! We can help ^_^