Hi there!
I'm also new to the forums, but saw this topic and thought I'd pop in, since my first tank was a ten-gallon molly tank. I would tend to agree with Ninjouzata on the tank size. I kept 2 female and one male balloon molly in my ten-gallon, and they seemed to be constantly stressed. Admittedly, at the time I had NO idea what I was doing, which probably attributed to a lot of the problem, but the fish were constantly agitated and bullying one another. When I finally lost one due to bullying, I had a friend re-house them in his 40-gallon tank and they mellowed out and began swimming together very quickly. I talked with him and a couple other friends of mine after the incident and they all said that a 10-gallon wasn't big enough for that many mollies (they thought I might be able to get away with just 1 in that tank, but understanding is mollies are relatively social).
Again, I'd like to point out I had no idea what I was doing, and I doubt my tank was ever truly cycled (was set up for about 3 months before I re-homed the fish and I did 50% water changes a week without ever doing an initial cycle), so the problem coulda been with any number of other things. Just figured I'd chime in with my experience and what my buddies had told me.

Whatever ya end up getting, I hope ya enjoy the fish, and welcome again to the forums!
