Mollie Tank...help!!

So I have a 20 gallon long tank that I decided to cycle with tetra safe start, I’ve heard great things and I usually cycle my tanks by fish less cycle. I currently have two mollies, the Dalmatian is aggressive and chases the other one and she shows signs of stress once in awhile and sometimes curls her tail a little ( I will most likely return her to petco tomorrow) the other mollie which is a ballon mollie doesn’t show signs of clamp fins but doesn’t swim as much. They both gulp at the surface sometimes and eat moss off the wood decor. Ammonia was at a light green but I’ve been using prime (so that could affect that) nitrites was at 0, and nitrates was at 5. I just completed a water change just in case and moved the filter higher to create more surface movement. Am I doing something wrong or just bought a bad stock from petco?

 

Molies can be a little fragile directly after you get them. I would recommend zebra danios. They are VERY hardy, and great for new tanks. In a couple months, after the danios help establish your tank, you could add more mollies. Though live bearers (in my experience) are hard to keep alive in a new tank. I would recommend getting 5 zebra danios.

 

Thanks for the advice but I’m trying to do a species only tank. I took the aggressive molly back to petco and the other molly has become very active. I think it was just them being new.

 

It could have been a combination of being new and there only being 2 mollies.

Mollies establish a hierarchy within their gender and males are aggressive breeders. So, the usual suggestion is have either only 1 of a gender or 3 and always have more females than males if you're going to have both genders.

If you only have 1 male and 1 female, the Male will constantly try to breed with the female and she'll be stressed because she can't get any down time. If you have multiple females, the Male will split his attention between them so each will get a break and some time to relax.

Sort of the same concept with the hierarchies within each gender. There will always be an alpha for that gender and the alpha likes to show that he or she is alpha. If the alpha only has one other of its gender to show off its alpha to, the alpha will bully and harass that one too much and it will get stressed and sick. If the alpha has 2 or more of it's own gender to show off to, it will split its attention between the 2 or more so each gets down time and the alpha gets to enjoy showing off who is boss.

Mollies are tough fish. I cycled my tank with tss plus, 4 mollies and a bn pleco and they alm survived. The main challenge with mollies is to get the right amount and mix for a peaceful tank and to decide what steps you'll take if there are fry.

 

Just a heads up about balloon mollies. I learned the hard way that they are highly prone to illnesses because of their body structure. They are massively inbred to get their unique body shape, and as such aren't as healthy as other types of molly.

That being said, I had one for several months that I absolutely adored (her two balloon friends lasted about a week before dying when I got them). She was the sweetest fish in my tank, always eager to swim to the front of the glass of anyone walked by. I nursed her through a nasty case of velvet, but a few weeks after that, she got severe swim bladder issues. It broke my heart to lose her; she had the best personality.

Sorry for the long story. I just didn't realize how horribly unhealthy balloons were before purchasing them, so I try to warn others when I can. As cute as they are, I doubt I will ever get another.