Some useful info for you about breeding platys (and other livebearers)
As I recently explained in another post, the population problem is the biggest issue. Any female coming from a pet store or any tank with a male in it is expected to be pregnant. Each female can have 3 - 4 spawns without a male in the tank... at a rate of 30+ fry every 30 days.
Each fish in the tank is passing waste, even the little fry when they are born. While the amount of waste the fry pass isn't the same as the adults, the number of fry makes all the difference in the world. While they are in there, waste will collect, sending levels up off the charts and making for a heavily toxic environment for all fish in the tank.
Space in a small tank also becomes an issue. My molly and Swordtail
fry are almost as large as the adults by the time they reach about 12 - 13 wks old... if you do the math, this adds up really fast. There simply isn't enough space or water in a 6 gallon tank to handle that. At present, your tank is already over stocked, and if you check ammonia, nitrite, nitrate, and pH, you will probably already see an imbalance. Checking only nitrate will tell you very little about what is really happening in there. Also, remember, nitrate is the end result of waste breakdown, which means it has to start with ammonia and nitrite. If there are living animals in the tank, there is ammonia going into the tank, this is unavoidable. Ammonia is toxic in any amount... which then breaks down to form nitrite... also toxic in any level.
The trick in maintaining a stable and safe environment is in providing enough volume of water to dilute the ammonia and nitrite, as they go through the phases of breakdown, while at the same time, providing enough nitrifying bacteria to break it down quickly. A stable and healthy tank will be large enough that once cycled, (where the bacteria population grows to eat the first waste that goes into the tank) the bacteria are populated enough and the volume of water is enough that the ammonia is being broken down immediately upon it's entry into the tank... and also the nitrites being broken down just as quickly. This will cause nitrates to build up, so frequent water changes are needed to then remove the nitrate.
Now, not only do you have a heavily overstocked tank, but now you have the wastes from birthing and the fry to deal with in there too. Like it or not, the simple truth of the matter is that those fish have to be suffering in there. You were already overstocked, then added another fish who gave birth to prob at least 30 fry... so even if the fry are now gone, the waste is still there. The only way I know of to keep a tank like that helathy is going to be stop feeding them and change 100% of the water every day. Put simply, your fish are going to die if you leave that many of those kinds of fish together in a 6 gallon tank.
When we decide to adopt a pet, even a fish, we have to be prepared to properly care for it. If we can't provide what it needs to stay healthy and happy, then we have no business in having that pet in the first place. Keeping any animal in a toxic environment is cruel, and qualifies as animal cruelty... something we here at FF don't condone in any way, shape or form. Those of us here on ff offering help to anyone needing it..., we give of our free time to do this, for free, for the sake of the animals. Our goal is to help anyone to properly provide for their fish byt explaining what is happening and how to best fix problems that may arise, and then teaching how to prevent them in the future.
We have told you a number of times now that your fish tank is way overstocked, asked for test results that you don't seem to be able to provide, and then went and added to the problem against everyone's advice. Stop for a sec, please, and think about what that says to us?? We are always here to help, but nobody here wants to be a part of the suffering and death of innocent animals, especially knowing it could have been avoided.
To do right by the animals you have now, they should be in about 30 gallons of water, with a heater and lots of decorations. They should be cleaned weekly with water changes and gravel vacs, and fed good, nutritious foods. If a larger tank is not something you can provide, then the right thing to do is to get rid of some of the fish in it now. Platys cannot live in a 6 gallon tank for very long without health problems. There is no way to avoid that. The average adult Platy
reaches 3 - 4 inches long. Take a piece of paper, cut out 4 of them, 3 - 4 inches long each, then hold them up to that tank, then tell me where you think those fish will go? The only thing that can
happen here is that the fish will suffer until they die a very agonizing death. Knowing that you likely have all female fish, at least 1 of them new and probably expecting another spawn of at least 30 fry within the next 30 days... this should give you an idea of how soon you need to act.
At the risk of sounding harsh, I refuse to advise anymore on this situation until I know that those fish are properly cared for, or that the effort is being made to make the situation appropriate for them. I don't have this kind of time to waste on watching someone purposely poison animals to death, for any reason, especially after that person has been given the help to make it right..