One more thing you need to learn and that is livebearer math.
Common sword tails reach secual maturity somtime between the age of 2 and 3 months. This means if you had a batch of fry born in march thay can already spawn. Now lets work with some small numbers. Lets say you have one female which gives birth about ebery month. So in lets assume you got 26 fry and 1.2 were female. So you now have 13 more females. The in May and June you get two more spawns awhich means 26 more femaler and a total of 39 (not counting what you had to start).
Now in June you have 13 more females born in March which could each give you another 26 babies or a total of 338 babies. But in July you add the 13 Apr. born females so you now have a total of 26 females that can give birth to a total of 676 more offspring. And in August to could be getting 1,014/month. Swords tend to make more fry in a spawn as they grow. And even if half of the fry in the above do not survive, half the numbers will still be a problem. Mysolutions when I kep swords were towfold.
I got angels to eat the sword fry. But eventually I discovered wild strains of swords and fell in love with the Montezuma. They are notorious fry eaters and will also stop spawning at time and then resume. The also have the longest sword all.
This is livelbearer math. Understand that nature's goal is not to overrun the world with the offspring of a single speacies. But nature is not stupid eithe. The smaller the % of offspring expexted to make it to adulthood means the greater number of them nature sees fit to have born at the start. Survivial of any species is a numbers game and most baby fish are food for something else.
For the livebearers nature added a twist. The eggs mature inside the female and free swimming babies emerge. This is a survival mechanism. I breed plecos and they are cave spawners and are raised to free swimming by the dad before they leave the cave. This is a similar strategy from nature which circumvents the problems of eggs being eaten.
And the above illustrates why things are often very different in nature and in a tank.