Is this normal for balloon mollies?

[HopeGR]

Four-month old tank owner of freshwater fish. Have a 20 gallon with 4 guppies. 2 bubble bee mollies, a platy and 2 male/female balloon mollies.

Out of those, the balloon mollies are my favorite by far. Bought the male/female Nov 2 and they were peaceful in the tank. Just today I went and bought 2 more male/female - moments of introducing them to the tank, the two males attacked each other! I was horrified. It's about 7 hours later and every time I check on them, I see them at it! Am I going to find them dead tomorrow?? So upset! Was I wrong to add the 2nd pair? And the 2nd pair happen to be bigger in size, slightly.

 

[Harriet]

not sure about balloon mollies as i’ve only ever had normal ones but it could be that there’s not enough space for them to avoid each other or they could just be fighting for the females if there is any i’ve only ever kept one male molly among many females and even he was a little aggressive sometimes

 

[HopeGR]

Re:

Thanks for the reply. I bought male/female thinking that they'll be better off paired. So it looks like the fighting has died down, meaning it's not as much. I feared they would kill each other overnight but, day 3 so far, and and they are still alive. I believe I've read 6 are the max. The first pair gave me a few babies three weeks ago, so I'm hoping the second pair will do the same. They are becoming my favorite fish.