Help - Balloon mollies losing dorsal fins

[RecChemist]

I have had my 10 gallon operating for 5 days. It includes:
1 paradise gourami
1 otocinclus catfish
1 panda cory
2 ballon mollies

that were staggered to not push the bioload. The mollies were added three days ago and this morning I noticed they were losing a portion of their dorsal fin. They show no sign of fin rot or any other illness and are still active and feeding. The other fish show no signs of fin loss or illness. I checked my levels and the nitrates(20ppm) and nitrites(.5ppm) seem fine. The hardness and pH are marginal but still within safe levels. Could these levels be the problem or is it something else?

 

[led_zeppelin]

yay, its not a pran post,

im thinking that your paradise gourami is nipping them, i once had a paradise gourami and it was beating the crap out of any fish that was in its water space, which in your case would be the mollies ( he wouldnt care about the rest of the fish because of there dull colors and the fact that they stay towards the bottom or on the walls), you might want to try a different gourami like a dwarf or something but lets see what everyone else has to say too...

 

[RecChemist]

Gourami nipping mollies

The gourami nipping the mollies was my first thought as well but I have not observed the gourami even chasing them as much as nipping. The gourami did chase them a bit the first day, but he quickly settled down. I have watched them all day today and have not observed any nipping.

The injury does not seem to be consistent with nipping either, it looks like a triangle pizza slice has been taken out of each dorsal fin.