Molly Fight.

[Ceramicbull]

I have 3 "Dalmatian" Mollies, one male and two female. Yesterday I added new fish to the tank. The tank is brackish so I added 2 Knight Gobies, a Freshwater Flounder, and a Nerite Snail. At the moment interspecies relationships are all peaceful. The bacteria are adjusting to the new bioload (perhaps a bit more than I should have), so the nitrates have a notable presence at the moment, but ammonia is still trace. I changed the water (~10-20%) this morning and probably will after work tonight, and will until the nitrates start to subside again. Hopefully all of this is just a sidenote, I include it incase the answer is "probably just stress."

My big female and male mollies started fighting about an hour ago. At first it looked like they were kissing, then spinning around each other rapidly. The female eventually got the better of the male, and started really going at his side and dorsal/anal fins. I didn't notice any damage, but it was surprisingly violent. I was afraid perhaps they were just hungry, but when I added a bit of flake, only the smaller female went for it. Thankfully nothing has happened since, and I hope this is just a dominance thing. The big female molly has a bit of a "lyretail" and is the only one who samples the mysis shrimp I add for the carnivores. I hope she doesn't have a taste for blood now or something.

Anything I can do to help other than the water changes?

C-Bull

 

[OldMan47]

Water changes are going to be need more often from now on in your tank because you have added to the biological load. Nitrates will never be controlled by biologics in a typical tank because there is no removal mechanism for them except the water changes. Nitrates are the end product of the bacterial action we call a cycle.
I have seen aggressive mollies before but have no idea how to stop it. The aggression often comes in short bursts and then subsides for a while just to happen again when something triggers the aggressive fish. It sounds like adding more fish to the tank was a trigger for yours. If your tank is starting to become crowded, that is often a trigger for aggression.