Balloon Molly being mean?

[Nikki773]

I have a balloon Molly and two red gold tuxedo guppies in a 10g tank. Had them for about 2 1/2 weeks now. When I got them the Molly liked to swim with the guppies and everyone got along fine. Recently I've noticed the Molly being mean and when I turned the light off he instantly stopped and went back to trying to swim with them, by then they didn't want anything to do with him. My question is... Why does the Molly get mean every time the light is turned on? I tried opening the lid with the light on hoping that the light not being directly on then would help but it hasn't. Does anybody no why he would be being mean only when the light is on and is there anything I can do to keep everyone happy. Tia.

 

[Nikki773]

Update: So now I'm noticing the Molly being mean even with the light off. So now my question is why is he doing this? Should I rehome my guppies and if so, would petsmart take them back? And what would I be able to put in the tank with the mean Molly?