The initial m/f ratio doesn’t matter after a month or so, because the offspring will be ~50/50%. In my experience, the population growth isn’t easily graphed. Females seem to have small first time litters with some still births common. I think this is because they often become gravid before they are finished growing to their full size themselves. Kind of like teenage pregnancies, it isn’t really good for them. But, as the females mature, and with successive litters, to a point, the litter sizes increase and the percentage of viable fry rises. So, while logic tells us at first that growth should be a standard exponential curve, the actual graph can go off the charts soon. Remember, Endler’s do not eat as large a percent of their offspring as do guppies or other livebearers. In short, you can’t depend on the population remaining in check without outside intervention, i.e., removing a portion of the offspring or introducing a very hungry predator (kidding!). As to the maximum population, it is driven as much by filtration as available space. Malaysian Trumpet Snails might help some with keeping the substrate clean, but I haven’t tried them myself. Just remember that fish poop increases as the fish population increases. Even if you’ve got the nitrogen cycle handling the cycle well, there will still be solid waste buildup.
I love Endler’s, and they adapt well to a wider range of temperatures than many tropical fish. But if you’re going to keep mixed gender populations, you might find yourself with lots of offspring you can’t get sell or give away. If that happens, please euthanize humanely. I recommend clove oil as the euthanizing agent.
