Dude, take your fish out and treat them, and all new fish. This way you know it is done right and you are parasite free. Some fish build an immunity and are carriers.
If you are fine with what is in your tank now, then just observe for velvet and brook or uronema, etc. I would only treat them if they show symptoms of that. I would assume your tank has ich even though they are showing no symptoms. There is no point in treating for ich if they are going into a tank with Ich.
I am just an advocate for prophylactic treatment of parasites so I will always try and convince people to do the right thing.