Aggressive Females-please Help Asap!

hI everyone, please reply to this and help me. I have had a female fancy guppy for a month and a half, and I have had a female gold platy for a month. I did a water change today (50%). I don't know if this effects my fish's behavior or not. my platy is hiding behind the filter and my guppy keeps coming up and biting her head. she tries to be aggressive and bites back. this has happened once before but they seemed to have solved it. my platy is not looking well. i'm sure she isn't pregnant, and the water is good quality. please help!!

 

What is the tank size? I would separate them ASAP.

 

What is the tank size? I would separate them ASAP.

 

Guppies shouldn't be on their own and I would put more platies in there too. I would move them into separate tanks, but it could be the platy is weak and so the guppy is biting it as in survival of the fittest. It could be dominance. Anyway, I would move them

 

Picture? Tank size, stocking, and exact parameters for ammonia, nitrite, and nitrate? Temperature?

Guppies and platies, while they do appreciate company, are fine on their own.