Female Molly Showing Aggression - Anyone Have Input?

[NeonBlueLeon]

Heya Forum,
 
I recently purchased two female mollies and a swordtail for a 20 gallon tank.  Today is their third day in the tank.  There are also five rummy nose tetras, but they are not an issue here.
 
So my concern is that one of my mollies is chasing the other molly and swordtail around.  It does not happen constantly, just periodically.  She would lunge towards the other fish's tail and the other fish would swim away.  This does not appear to be a territorial issue as the fin-nips occur sporadically wherever she is in the tank (no observed damage to any fins yet).  I do not think either of the mollies are pregnant since they were kept separate from the males in the LFS, but honestly who knows.
 
Could this the molly trying to establish a pecking order in the tank?  Or perhaps she is bored?  My tank has a mix of dark and light gravel, live and fake plants, a bubbler, and a weak current (from the filter).  I just noticed this behavior today.  Their first day, the two mollies and swordtail looked scared, the second day they seemed to be exploring and swimming around.  Miki (the fin-nipper) leaves the rummy nose tetras alone.  (On a side note, my beautiful red swordtail occasionly swims into the school of tetras, and they appear to communicate.  The tetras just hang around with the swordtail for around 30 seconds, and then they resume their business.  It's really neat!)
 
Just to make sure, I checked my water params as well.  Ammonia is 0, Nitrites are 0, Nitrates are less than 5.  The water temperature is around 72-74 degrees Fahrenheit.
 
Has anyone experienced this behavior before?  Does anyone know the cause?  Thanks in advance!

 

[cowboy507]

Could be like you saidm the fish is establishing dominance

 

[the_lock_man]

This was one of the first queries I ever posted on this forum.
 
If my experience is anything to go buy, some mollies are just vicious, and the aggression won't just disappear.

 

[DyArianna]

I have a female black marbled lyretail mollie who is just a little brat!  She was the queen bully of the tank... but now one of her fry that is also a lyretail has taken up the role as well.  I added a couple of males to the mix thinking things would calm down and they did for a few days but now back to the old ways.  However, now I have 3 bullies.  The two lyretails and one of the male dalmations.  Can't win!  lol  Just now working on adding some more places in the tank to break up the line of sight... allow for hiding, etc.  Will see if this helps. 

 

[NeonBlueLeon]

Thanks for the replies, everyone!  I really appreciated it.

 
Unfortunately, the bullying has gotten worse.  No nipped fins yet, but I feel like the victims are getting stressed.  A few days ago, the chasing was periodic, but today it happens almost every few seconds.  I may need to return her to the LFS

 
Edit:  I forgot to mention, there was an Ich outbreak in my tank.  They are undergoing salt and a little heat treatment at the moment.  Perhaps the parasite and changing conditions are causing the aggression.  If the aggressions doesn't go away after things return to normal, I'll have to considered relocation.

 

[Arcticfox1977]

The only time I've seen my mkollies doing this at feeding time and shortly after. However 1 of my platys loves diving for the other platy. Again, just now and then.