I gotta say, I can't recommend a fw
dip. Alot of fish are so stressed out already that it can help to kill them. Just wait the couple more hours. Unless the fish can't breathe or is on deaths door at this moment.
Alot of people say they are great but just as many say they can be bad. theres not much opinion in the middle.
You can use tank water from your main tank or fresh saltwater. If you don;t have a cycled qt or an extra filter running in your main tank then you are gonna have to do water changes anyway while you medicate.
How many fish do you have and how many are infected? I;m not sure about parasites but wouldn't all your fish now be suscecptible to whatever it is?