One had Ich and brought it to your tank. It just took the move to your tank to stress/weaken him enough to let the Ich get the upper hand. There are 4 stages in ich's life. The only one you can see is the pregnant one.
Those white dots you see are the pregnant ich. It takes About a week of being infected to see those. So, if you say the spots appeared a day later, it was already infected.
Hyposalinity is when the salinity/specific gravity of the water is lowered to 1.009 over a period of a few days. Then kept there for 6-8 weeks. It will kill the ich. I can explain how if you want to know.
There are other methods also, copper treatments work faster, but are real hard on the fish.
BTW, neither hypo or copper can be done if you have Live Rock or Inverts. You must separate the fish in a Q/T.
I have a thread chronicling my hyposalinty treatment.
http://www.thereeftank.com/forums/sh...d.php?t=124438
I am at the 5 week mark on 1/31.