Aggressive Black Molly

[schmorrell]

I recently installed a 20 gallon tank, conditioned it over a couple of days, and today I purchased my fish: 3 mollies (black, balloon belly, and dalmatian), and 5 neon tetras. I also added 4 tablespoons of conditioning salt and a fake plant and sculpture. I'm running a filter and have a heater as well, keeping the temperature at 78 degrees Fahrenheit. Other than a few goldfish as a child, this is my first venture into the world of fishkeeping, and I am trying to be as conscientious as possible. Although the Petsmart workers couldn't guarantee that I got three female mollies, they helped me choose three whose anal fins were more splayed out, saying this was an indicator they were probably females. I wanted females because I didn't want them breeding and I also didn't want the males badgering the females or fighting each other. My concern here is that the black molly is fairly aggressive. Whenever I put my hands in the tank to let them nibble on my fingers, the black molly chases away the dalmatian and generally picks on her. I've also seen the black molly chase the balloon belly, although her(?) favorite target is the dalmatian. When I fed them tonight, the black molly turned almost violent. I can't tell if she is actually nipping at the dalmatian or just knocking her away. I am worried the black molly will injure/kill the dalmatian, even though the pet store said they were non-aggressive. Any ideas on how to alleviate the problem? I have enough room currently for one more molly if the addition might calm things down. I posted a video of the fish on youtube if you care to watch to help assess the situation.
Any feedback is appreciated.
Thanks,
Con

 

[OldMan47]

Welcome to the forums Schmorrell. You were correct in your verbal commentary that you have all females. They will have fry anyway because a female molly can store sperm for up to 6 months and continue to have one after another fry drop during that time. I am not seeing any aggresssion in the recording that looks like it would cause any problems. I am glad to see that you are following the advice you were given on caring for your fish. Unfortunately, that advice was seriously flawed. You should not add any fish to that tank until you can get it cycled.
If you can, I would return all of the fish and follow the instructions in the "New to the Hobby" section on how to do a fishless cycle on your tank. If you can't return the fish, you can embark on what is called a fish-in cycle. This can be done with success but is a lot more work than a fishless cycle. There is a link on how to do one in my signature because I encounter at least one person every day who has been given the bad advice that you were. The fish-in cycle typically takes from 4 to 6 weeks and requires some amount of water change daily to keep the water safe for your fish. The new water that you add needs to be treated for chlorine and needs to be about the same temperature as the water in the tank. By contrast you will do 2 or 3 widely spaced water changes and not worry much about temperature for a fishless cycle.
An essential tool for doing a fish-in cycle or really any cycle is a liquid reagent based test kit for ammonia, nitrites, nitrate and pH. The paper test strips are considered almost worthless for this kind of testing and end up costing just as much in the long run because the liquid test kits last a long time.