Tank too small?

[Elle2]

Hi,

I have recently added two mollies (one black and one sailfin) to my tank and notice that the Sailfin is quite aggressive. I have not been able to find any information about this - everything I have read says they are pretty good community fish.

His aggression largely takes the form of chasing all other livebearers (guppies, platies and the black molly) - regardless of sex and species, for what seems to be the purpose of breeding.

The guppies(2) and other molly are male, and the 4 platies are females. I only have a 20 G - is this too small for him?

 

[theotheragentm]

If it's not a long tank and just a standard one, you might be squeezing them in a bit too tight for swimming area. While community fish are generally okay with other community fish, some fish have different personalities which makes them bullies. You may have to separate them.

 

[David14259]

You could try rearranging the decorations of the tank. This will help disrupt any terroitories that may have developed.

 

[Bubble_B0y]

from experience - mollies are nippy in small groups
Usually the biggest molly will bully and chase smaller mollies.

Since your tank is too small to house more mollies.
I would take that bully back to the fish store.