Good to heed the advice given here- but I would suggest not cutting corners. If one fish has ich, then all "have it" even if they don't show signs. In reality, ich spores are common- but healthy, unstressed fish typically don't "come down" with it.
So- I you have fish in a tank- and some show it, they all are "contaminated". Assume they all have ich.
Raising the temp is the most effective and consistent treatment. The addition of some salt can help (personally I believe this is due to the slime coat being stimulated).
As far as the cycle is concerned- Ammonia is bad at any detectable level (with a good test kit). Anything above .25 (1/4 of a part per million) begins stressing fish. It is the inconsistent and spiking levels of ammonia, nitrates, and nitrites that cause huge stress to fish- and it often leads to many fatal conditions, including ich.