female molly and male platy fighting

Question
QUESTION: I inherited an aquarium from my son who has gone off to college, and until then I was completely ignorant of anything having to do with aquariums.  The tank they are in is TOOOOO small and so I am trying to get a larger tank up and running (cycling without fish), but it has only been up for one week. One of the reasons I have purchased and planted a new tank is because the male platy is very aggressive towards the female molly.  She has sustained ripped fins and has a large scrape down one side and she spends most of her time trying to get away from the platy.  What concerns me is, what I think is just a scrape may be something else that I am not recognizing.  The molly is still swimming and eating and moving well, but I am concerned.  The small planted tank has the molly, 3 platys, 1 cory cat, 1 oto and 5 neons. I have read that she needs more brackish conditions but I understand the salt will kill some of the other fish and is not great for the plants.  The little tank has to have water changes almost every other day because of the overcrowded conditions.  Suggestions?

ANSWER: Hi Laura,
Your setup is good and sounds like you are quite knowledgable.  The tank is set up correctly and maintained correctly.  A planted tank is best for fish especially the neons and frequent water changes will lower daily toxin levels in the tank.  But I dont think you have to change it every other day.  Even if the tank was a small 5g or a 10g, you can extend it to weekly.  The fish you mentioned all stay small and do not have a large bioload.    

A brackish setup is not required for mollies but they can tolerate salinity conditions which is why they are also used in saltwater cycling.  And you are right about salt not being good for plants, it will turn them brown.

Are you sure the molly is a female?  Male platies and mollies are aggresive towards other males and will frequently chase the other around.  I would suggest seperating the two or upgrading the tank.
-Matt-


---------- FOLLOW-UP ----------

QUESTION: Ms Molly had babies several months back while my son was still here, so yes,
I am sure that she is a she.  The male platy is so rough with her and will
smash her into the walls of the tank and into the decorations.  She hides most
of the time except for feedings.  That is why I think she has the white scrape
down the side, but again I am not sure I would recognize a fungus or other
disease.  Her stress levels have got to have sky-rocketed.  I have seen him
tear her top fin and tail.  He is not much better with one of the female platys
but the other one he ignores.  Will this aggression carry over from the 5 gallon
to the 20 gallon tank?  He's a pretty little fellow, but I wonder if finding him a
new home is in his future.

The ammonia levels go up quickly in this tiny tank, although the nitrate and
nitrite levels are fine.  that's why the water changes are so frequent.  I am
trying to push the cycling through quickly on the 20 gallon tank, but it's only
been a week.  I have nothing else to move the molly into.

Answer
That is one quite aggressive male platy.  It will be a hit and miss if you move him to the 20g.  Because of a such larger space compared to the 5g, there is a good chance she will be away from him most of the time.  But if the same aggression occurs in the 20g then I would separate one of the two.  

If you want to increase the rate of cycling on the 20g there is a few things you can do.  Raise the temperature to 80F.  You can "seed" it, seeding means transferring an item from a healthy established disease-free into the new tank.  Items such as filter media which is saturated in beneficial bacteria necessary to give a new tank a head start.  You can also use gravel, decorations, live plants and etc, but filter media is the number one best item to seed with.  Also, be sure you are adding a source of ammonia for the new tank to cycle.  No ammonia = no food for the beneficial bacteria to grow = no cycling.  A source of ammonia either by fish food, fish, or straight ammonia itself.  
  
For the scrapes, there is a medication called Melafix.  It is used to heal cuts and scrapes and has great reviews.  

Let me know if you have any further questions.
-Matt-