This is how I treat White Spot
first of all, Its not worth it to quarantine the fish as the main factor of Ich is stress, caused by poor water quality, poor stocking, etc. and if one fish has a low enough immune system to get it then its possible that the other fish can easily get it too, so there really is no use in quarantining the fish.
1. find the cause of the disease. what is the stocking? how large is the tank? how often do yo do water changes and how much? do you add anything like PH up or down? Is the tank cycled? do you change the filter cartridges, or clean them out in tap water?
2. If you have fish that can be placed in tanks with salt then It would help to add some Aquarium salt, if you have cories, or other scaleless fish then salt would be a bad choice
3. Raise the temperature to 84-85, raising it to 82 will speed up the life cycle of the parasite, but in a higher range if 85, it will kill it off, and prevent the parasite from reproducing
4. Add the proper medications to treat the fish. The one that lock man suggested works great
5. If the disease progresses then it will help to give the fish "salt baths"
To administer a salt bath
Mix 1 teaspoon aquarium salt with 1 gallon of treated water (not tank water), make sure all of the salt is dissolved. You can then poor the gallon into smaller containers if you are treating multiple fish. The salt bath should be the same temperature as your tank, so your fish does not get shock form temperature difference as well as salt.
Scoop your fish into the salt bath and leave them in 5 minutes, unless the fish goes unconscious (rolls over on side and gill movement slows).
After the 5 minute period mix tank water into the bath to get 2/3 tank water, 1/3 bath. Leave them there for 10-15 minutes, ten return them to the tank.
salt bath info from this site - http
/www.bettafish.com/showthread.php?t=25297