Mollies And Platy Concerns

So, I want a few different opinions on how I can better manage my fish. I have two mollies and one platy (black molly, yellow potbelly molly hybrid and red wag platy). The Black molly seems to be causing most stress on the other two, as he is very aggressive when near the other two (especially the other molly and when it's feeding time) as he harasses and nips at them. The yellow molly is basically the same size as the black and the red wag platy is considerably smaller.

My question is how do I ensure they all get along without investing in a larger tank. I have a 5 gallon "" that does a great jump keeping the tank self-clean even though I clean it about every other week. Also some concerns on the platy doesn't seem as active when introducing the 2nd molly (the yellow molly discussed above). The platy just stays in different corner towards the top. Before he got along with the black molly.

 

Welcome to Fishlore!

Unfortunately, a 5 gal is too small for mollies, and arguably a platy as well. Mollies can get to be 5" long and have a high bioload, so they should be in a 29 gal tank minimum.

The issue is unlikely to improve in such a small tank.

What sexes are the mollies?

 

They need a bigger tank. Platies need a minimum of 10 gallons, and mollies need a minimum of 29 gallons. 5 gallons is not enough.

 

No idea how to tell sex of each fish. Any ideas or easy ways?

 

Yep!

:

 

You can also take a picture of it and post it here if you're not sure.