silver molly and neon tetras

Question
hi my name is carly i have had tropical fish before but i have set up a new tank about 2 weeks ago and there is 2 female swordtails and 2 silver mollies i think one of them is pregnant this is the one that has killed 4 of my neons could you tell me a reason why she has done this to them also she is bitting the other female molly please could you help me thank you

Answer
Carly,

 First question is are you sure it is a female molly? They can get aggressive when they are going to give birth or one could be male and the other female. As for why she is killing the other fish is not really known. Some fish are more aggressive than other and sometimes you just end up with a bully. Have you tried taking the molly in question out of the tank to see how the other fish handle thing? Sometimes you can put some fish together and then sometimes you can't. Unfortunately it is a hit and miss with fish sometimes. To save heartache, I recommend removing the molly from the tank.