Why are my platy and molly bullying each other?

Info about my tank:
70 litre that's been running for about three months and has been cycled. It has 11 baby guppies, 1 female molly and 1 male platy.

Lately Ive noticed my molly and platy chasing each other around the tank. They will ram headfirst into the other's side/head. Whenever the platy does it to the molly, she will start to shimmy. They do this for a while then the platy goes and 'sulks' in the plant. I thought that it might have been because the molly was pregnant but she gave birth and they still do it.
I don't think they're playing either because I saw a tear in the molly's dorsal fin yesterday.


Are they bullying each other and why are they doing it?


Sorry if I did not provide enough info. I'm still new to forums.

 

HI Rhonda and welcome to Fishlore!

The molly might be secreting hormones signaling that she is ready to give birth again soon. I can't be certain, but it might be possible that the platy wants to try to eat the fry as they are coming out of the molly. I've seen fish follow my livebearing females when they were giving birth and eating the fry right away.

 

Thank you Beeker.
She only gave birth 2 weeks ago. Would she already be pregnant? I know it is possible but would she be giving out hormones already?
I just found a bite in my platy's tail too.
Should I separate them? I don't want them getting hurt.

 

She could still be pregnant.
Female mollies can store the sperm packs for 6 to 10 months.
It would probably be best to separate them.

 

Will a homemade breeding net be alright? Ive heard you shouldnt leave fish in there for too long though. If not, what else could I use? I can't buy another tank.

 

You can use a tank divider.