i used a freshwater dip on my yellow tang that developed black parasites. it will work different for different illnesses obviously, but for my tang it worked great. i dipped him in in freshwater for about 2 minutes and when i took him, most of the parasites were already dead and had dropped off him. 10-15 minutes is way too long to be freshwater dipping so just make sure if you do that to do the half and half method that two11devan used. thats my experience, he seemed fin afterwards and currently he is very healthy. hth
steve