I agree with you that poeciliads aren't as tolerant of poor water conditions as most of the resources seem to say.
However, the quarantine tank is essentially cycled as I started it with 2 filters (HOB and sponge) from an established tank. Ammonia and Nitrites have been essentially zero ( there were some small spikes of total ammonia of .25ppm, with free ammonia being less than .02 ppm, so for all practical purposes it's been zero all along) for 2 weeks. I test every day and don't expect to get any different readings in the following weeks. I don't think that this is the problem.
The fish came from a dirty pet store tank and went into a clean QT with much better water conditions. When I go to the chain stores, about 2/3 of the platies are already hovering in one place with clamped fins. It was probably foolhardy of me to purchase any fish from these stores, but there really aren't that many options. There is only one store in my tri-state area that actually has tanks without dead and diseased fish, and they charge $8 for a platy or tetra. I will be going there next, as obviously it's worth the extra cost.
I do think that I made a mistake in adding too many different kinds of fish to the QT at once. I think that the social dynamics may have stressed the fish that died. I believe that he probably had a latent infection and it got may have gotten worse with stress. From now on I will be limiting the number and type of new fish that I quarantine at one time.
The other fish look completely problem free, with the exception of one who is slightly slower than the others. I am worried that he may develop the same thing the now deceased fish did. That's why I am looking for an appropriate med so I can be ready.
I am tired of posting on these forums with a problem and having people tell me my tank isn't cycled. Even if the tank wasn't cycled, if my ammonia and nitrite readings are 0, then it doesn't matter. If the tank wasn't cycled, then the way to deal with that would not be to wait and see if all the fish die, but rather to test ammonia and nitrite daily or every 12 hours and make large water changes to keep both within safe levels.
Funny thing, the fish that went into shock isn't the one that died. He is the one I am worried about though.
Hopefully there will be no more deaths.
I didn't tell you that you're tank wasn't cycled, because obviously I'm not there to have any proof otherwise, I was simply quoting what you already stated. And the reason I suggested 'waiting it out' was simply because it would be inconvenient to buy medications for fish when you don't know what to treat specifically, especially considering you have fish who are or were displaying different symptoms than the others; that could make it harder to diagnose. As you stated, hopefully there will be no more deaths.