I don't really understand your question/post. You say you had a sick platy, then you just mention that many had signs of ick and you treated with ick.....
In the future, if you see one sick fish in a tank, don't just leave it in there. It will sometimes make your entire tank sick.
Did you use any meds together? Some are ok. to use together, some are not. Did you combine a ick medicine with the "all in one" medicine? Can you give me some ingredients of the medicine you used together? I personally don't have a lot of experience with whitespot....but im sure you can easily find a solution on this forum or google, most people recommend turning up the heat to 86 and adding salt, and doing lots of PWC
, personally I would put an ick medicine in the water as well like Malachite or Acriflavin.